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Thread: Tuning 40 DCOE Weber 151 on an L24

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    Supporting Member Zedyone_kenobi's Avatar
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    Default Tuning 40 DCOE Weber 151 on an L24

    Installed my 40 DCOE webers on the L24:

    Engine specifications
    2.4 liters original motor/head/cam.
    Pertronix ignition
    Pertronix 1.5 Ohm coil
    MSA 6-2-1 headers

    adjusted idle mixture screws 1/2 turn out
    Adjusted all idle speed screws (without actuator rods hooked up) until they were about to uncover the first progression hole

    I had at my disposal, an wideband O2 gage installed into my header (innovative LM1)


    and a Air Sychronizer tool with weber air horn adapter
    (note, air horn adapter not shown)

    My factory out of the box settings for my 40 DCOE 151's were:

    30mm venturi
    130 main Fuel Jet
    170 Air corrector
    F11 Emulsion tube
    55F9 idle/slow running mixture jet

    Car would not start at all. It would run off of the gas put out by the accelerator pump, but would not stay running. I kept increasing the air fuel mixture (note NOT touching the idle speed screw at all) until the car would start and stay running. This ended up at 2.0 turns out from fully closed.

    At this point, you MUST let the car warm up to operating temp. After the car warmed up, I was getting an AFR of 10.1 on the LM1. Too Rich. Mr. Franck's of side draft central's white paper points out we should always aspire to 12.5 with our DCOE's. Well I managed to get it to be there running about 1.5 turns out from full close don the air fuel mixture. Car ran smoother like this as well.

    Initial drive was very promising. However, the dreaded flat spot did exist in the transition point between my third progression hole and when the main circuit came in.

    I dove back into the side draft central white paper, and a way of getting the main circuit to come in faster is to reduce the size of the air corrector. You see the air corrector is like a vacuum bleed off. In order for the main circuit to work, you have to get the column of liquid up the emulsion tube and down to the venturi. This is done by way of sensed vacuum from the engine. See 3rd picture on the left.



    The larger the air corrector the more engine vacuum is bled away and it takes more vacuum to pull the fluid up the emulsion tube chamber. Capillary action only gets you so far, and often the stumbling effect is the engine vacuum is too low to effectively make the transition from progression circuit to main. This should happen at about 1400 rpm according to Mr. Franck.

    Upon driving around I noticed that my part throttle, 4th gear, low rpm (2000 rpm) steady state cruise I was reading about 15.9:1. This is too lean, BUT I knew that running 130 main jets which are really a bit large for 400 cc of displacement I did not need to richen up the main jet. So instead I put in 160 Air Correctors,down from 170. I touched nothing else, and went for a drive. My flat spot on transition was greatly reduced and even eliminated in 1st gear. But was still present on all other gears. However the lean stumble was smaller and the main recovered quickly.

    I bet your wondering, Hey Zedyone, what about your floats? Well I am not going to change anything else until I check those.
    Let me make one thing clear, you should always check your floats BEFORE you do any tuning. The float level can drastically effect how and when your main circuit comes in, as a low float level will increase the distance the fuel has to travel up the emulsion tubes.

    I purchased the Keith Franck float measurement tool off side draft central webshop. I will be trying to see where I am this week. It would be foolish to spend any more money until I check the float levels.

    Also, not mentioned here, but I did check the air flow through the carbs for balance with my sync tool pictured above. Right off the bat with the engine warm, they were within 0.5 of each other on the tool. So I left them alone. If I wanted to change that, the only way to make fine tuning adjustments between the carbs is to adjust each idle speed screw located on the side of each carb. I did check balance on both barrels of each weber individually and the flow was identical on all three carbs. Weber does include a way to balance each barrel of one carb individually, but I figure that adjustment is probably to make up for some external imbalance, be it rings, seals, etc. If the butterflies on one carb are open the same, then the air flow should be the same. If they are different, there is an external reason. New webers the air flow should be identical.

    When I check my floats, I will post pics and report back.
    1971 240Z HLS30-38691
    93.9% done and getting better every day
    Now with 100% more DATSUN SPIRIT L28 Power
    1968 Datsun 2000 SRL311-03416

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    Registered User d240zx2's Avatar
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    :-) :-)
    First & Third owner of HLS30-00721
    B. 01/70 D. 03/12

    New owner of HLS30-15653
    B. 12/70 D.

    Frank in Houston, Texas

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    Marooned Fish cygnusx1's Avatar
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    The carburetors that keep on giving. I love them too. I don't use an AFR gauge, although I should. Here is what I discovered, the L loves to idle rich, and the popping in the exhaust during deceleration, if you have it, goes away completely, if you throw in a half turn more idle mixture, after you have found ideal idle. Counterintuitive...

    Yes, fuel level is CRITICAL to the timing of the main circuits.
    Last edited by cygnusx1; 04-30-2012 at 04:49 PM.
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    Supporting Member Zedyone_kenobi's Avatar
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    Behold the Keith Franck Weber float measuring device! This goes into where the emulsion tubes go. All you do to check the real float level, is to remove the round jet cover, and then unscrew one of your main jet/emulsion tubes. You run the car and in bright light, you can slowly stick the end down into the hole. IF you look carefully, you can see the fuel come into contact with the tube as you stare at the end of the tube. Keith says to do this is bright light and he was right.

    I did this very quickly, and did not measure the distances, but my first carb (the one nearest the front of the car) showed the line on the tube several mm below the white sleeve meaning the fuel level was LOW. My second carb indicated contact with the fuel before the line ever came into view, indicating a HIGH fuel level. The third carb again indicated low, meaning the indicator line on the acrylic tube was below the white sleeve.

    This goes to show you that the factory settings are merely 'in the ball park' of right. Not at all the ideal 25mm from the top surface.

    Do not fret the double lines on the tube. The are just 25mm from either end, so it does matter which end you use.

    I like this method, and I will adjust my floats when I have a couple of hours to dedicate to the job.

    Great products here by Keith Franck.
    1971 240Z HLS30-38691
    93.9% done and getting better every day
    Now with 100% more DATSUN SPIRIT L28 Power
    1968 Datsun 2000 SRL311-03416

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    Registered User LeonV's Avatar
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    I've got the same tool, but haven't put it to use yet. It's very clever!
    2/74 260Z

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    Zedyone_kenobi
    I think you are having waaay to much fun with this!! I'd also guess that by now you have spent at least as much on your Z as you originally paid for it. Another sign of serious addiction...

    Next step - - individual throttle bodies with F.I.... Yes, the path you have chosen always leads to a next step... When you run out of things to do to your Z - - - - you'll be looking for a 911 next...

    At any rate -keep up the good reports.
    FWIW,
    Carl B.

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    Registered User LeonV's Avatar
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    I can attest to that next step! Unfortunately, I missed out on a set of HKS ITBs but I'm on the prowl!
    2/74 260Z

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    Supporting Member Zedyone_kenobi's Avatar
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    I think my addiction comes from my inherent need to improve things. I have not added all my receipts and I dare not attempt it. But yes I have spent a bit but not as much as some (denial is what stage of addiction, I forget)

    I think my car and I are about average in the Z world.

    I am having a blast. A z is such a beautifully simple thing. I love working on it.

    I will try to get accurate measurements of my float levels tomorrow and report back.

    Anybody know how many times you can reuse float bowl gaskets?
    1971 240Z HLS30-38691
    93.9% done and getting better every day
    Now with 100% more DATSUN SPIRIT L28 Power
    1968 Datsun 2000 SRL311-03416

  9. #9
    Registered User d240zx2's Avatar
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    At least once.
    First & Third owner of HLS30-00721
    B. 01/70 D. 03/12

    New owner of HLS30-15653
    B. 12/70 D.

    Frank in Houston, Texas

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    until they start leaking.

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    Supporting Member Zedyone_kenobi's Avatar
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    Today I redid my cable linkage and set the floats to dead on 25 mm using my gage. Since I raised all of them (number 2 was actually low as well) I would imagine that my mains should come in sooner.

    I will also predict that I will probably be far richer at cruise as well.

    I will let you know how it is running Monday
    1971 240Z HLS30-38691
    93.9% done and getting better every day
    Now with 100% more DATSUN SPIRIT L28 Power
    1968 Datsun 2000 SRL311-03416

  12. #12
    Supporting Member Zedyone_kenobi's Avatar
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    Initial test drive indicates my transition stumble has taken another progressive step to non existence. I drove it without even taking the AFR gage out of the glove box to see what I was running and I was very pleasantly surprised by the smoothness of the throttle. AFR results to come on Monday.

    But setting the float level definitely helps in getting the mains to come on sooner. Very happy I did this. Everything you read about tuning webers says Do the float levels first. Now I see why, the difference from factory set to dead on is substantial. The transition from progression circuits to mains is almost imperceptible. I think if I were to go down on my air corrector again, and then see what my AFR are, I will be in business, but for now, I will leave all alone until I get it on the highway to see what my 4th gear cruise AFR is.
    Last edited by Zedyone_kenobi; 05-06-2012 at 02:04 PM.
    1971 240Z HLS30-38691
    93.9% done and getting better every day
    Now with 100% more DATSUN SPIRIT L28 Power
    1968 Datsun 2000 SRL311-03416

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    Registered User d240zx2's Avatar
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    4th gear? Don't you have a 5 speed yet?
    First & Third owner of HLS30-00721
    B. 01/70 D. 03/12

    New owner of HLS30-15653
    B. 12/70 D.

    Frank in Houston, Texas

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    Supporting Member Zedyone_kenobi's Avatar
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    Your killing me Frank!

    I just bought a new rebuilt type B 4 speed from zcarsource! The day I have a 5 speed will probably be the day I trade the numbers 2-4-0 with 9-1-1
    1971 240Z HLS30-38691
    93.9% done and getting better every day
    Now with 100% more DATSUN SPIRIT L28 Power
    1968 Datsun 2000 SRL311-03416

  15. #15
    Registered User d240zx2's Avatar
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    Get a ZX 5-speed. You will NOT be disappointed, especially if you plug in an R200 3.90. I promise!
    First & Third owner of HLS30-00721
    B. 01/70 D. 03/12

    New owner of HLS30-15653
    B. 12/70 D.

    Frank in Houston, Texas

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    Registered User LeonV's Avatar
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    Quote Originally Posted by d240zx2 View Post
    Get a ZX 5-speed. You will NOT be disappointed, especially if you plug in an R200 3.90. I promise!
    Agreed. It transforms the car!
    2/74 260Z

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    Supporting Member Zedyone_kenobi's Avatar
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    I drove the car again for some pleasure cruising, and I can say I have absolutely NO flat spot or hesitation. Fixing the float levels did more than anything else did. The car drives wonderfully. I still do not know if my AFR is spot on as I was enjoying the drive and feel and sound so much I did not even take the gage out of the glovebox. But final jetting still needs to be verified, but I am darn close now, I may just leave it alone until I get these on my L28.
    1971 240Z HLS30-38691
    93.9% done and getting better every day
    Now with 100% more DATSUN SPIRIT L28 Power
    1968 Datsun 2000 SRL311-03416

  18. #18
    Registered User madkaw's Avatar
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    Time to go to the dyno with some extra jets in hand and get all you can out of the mighty L24.
    Steve
    71 240z,bw-5sp 2.4-40 over,balanced,e-88,big valves,ported&polished, stage2,header, triple Mikuni's 40's
    3.90 Subaru STI LSD

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    Better yet- do the STI. LSD diff for the real transformation
    Steve
    71 240z,bw-5sp 2.4-40 over,balanced,e-88,big valves,ported&polished, stage2,header, triple Mikuni's 40's
    3.90 Subaru STI LSD

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    Stephen, I followed in your footsteps the past few days! Thanks for your help. The car is coming along fine.

    I figured I'd just append my data and observations to this post for future enthusiasts following in our footsteps.


    Build:
    motor: L24 0.75mm overbore
    head: Maxima N47 with stock valves
    headwork: medium porting/shaping intake and exhaust
    cam and valve train: Delta 0.46' lift and 270/280ish
    Carbs: 40DCOE 151
    Intake: Cannon Long Runner
    K&N filters
    Stock 240z mechanical pump dead headed.


    Carb Internals:

    Idle Circuit:
    Jet: 55F11

    Main Circuit:
    Jet: 125 F11 170
    Main Venturi: 30
    Aux Venturi: 4.5

    Acceleration Circuit:
    Spill valve: 50
    Jet: 45

    Starter Circuit:
    Jet: 85 F9 150

    Needle Valve: 225

    All new gaskets

    ZX distributor set 17degrees at 900rpm no vacuum advance


    Notes:
    - the long intake and big air filters barely fit....but they do! I have to pull the master brake cylinder out to measure the airflow into #5&6 when balancing with synchronometer

    - As Stephen mentions, the fuel level is crucial for smooth idle-to-main transitions. My default fuel depth was 29mm down from the main jet well's top. I noticed a bit of a transition bog. When I set the fuel to 24.5mm/24.5mm/25.0mm for the three carbs, the bog disappeared...but I got fuel dripping between the throat and the main venturi on a couple of the intakes. This did not happen at 29mm fuel depth. I will re-check the fuel depth but I think it is a combination of Aux Venturi to body sealing, the stock fuel pump pressure and the too-big 225 needle valves that came with the rebuild kit. I will experiment on resolving and report back.

    - initial setting of the carb's primary two interacting and adjustable parameters was my biggest hurdle (Thottle Valve opening and Idle Mixture Screw depth). From what I read, the importance of setting the "throttle valve as close to blocking the first progression hole" was the priority. I was able to view the "blocking" through the inspection port over the progression holes and easily make it the same for all 3 carbs . The problem is that I could easily block the first hole and have the left (with respect to (wrt) the car) edge of the throttle plate anywhere from the right side of the hole and beyond. I initially decided (incorrectly of course) that it was important to block as much of the first progression hole yet let a wee bit of air around so I set the throttle plate so that the left side of the plate was at the midpoint of the first progression hole... then the problem began... in order to get the car to run, I had to set the idle mixture ~3.5 turns out but it ran pig rich and it was hard to get the RPM's below 1100. It ran smooth and idled smooth and had lots of power but it was too rich and stinky and it would sometimes diesel after shutoff. It would not run at 2.5 turns out!!! After a lot of experiments I re-started from scratch, but this time, I set the idle Mixture Screws at 2 turns out then adjusted the Throttle Valve opening to get 900rpm idle. It worked much better. I am still playing around but it is how I would recommend others to do initial setup. I am now reading the plugs and not using the WB just like Stephen above with 2.25 turns out, the plugs are looking much better... a touch too lean but some brown on the porcelain. I have read that webers like richer and I experienced it so I will continue to experiment. The only "stumper" is that I did not expect the idle mixture screw and throttle valve to have such an effect on lean/rich... I thought it was the idle jet selection. I guess the pressure dynamics at the progression hole affects how much fuel comes out pre-idle mix screw. With more of the first progression hole exposed to manifold vacuum at idle, less fuel is needed from the mix-screw path...AND less fuel can reach it as it will leak out the exposed progression hole and not flow further to the mix screw.

    - setting the throttle push rod arm lengths.... don't do it on the carbs using the turn buckles!!! All throttle arms should be the same length. Set them on a bench using vernier calipers. Simply stick the tangs of the calipers in the heim joints balls and set the length then set the locknuts. The way to adjust the cannon throttle push rods is to loosen where they bolt to the main rod. You can tighten with the car idling and easily hear if you push them down and increase the idle.

    - I set the Air bypass Screws in all the way then adjusted as needed to get all of the carb throats to flow the same using the synchronometer. I think the value was 5.5 on the dial at 900 RPM.

    - There is a stop bolt under the acceleration pedal on a 240z. I set it so that the pedal stops before it pushes the throttle valves past their stop... otherwise at WOT you can run the risk of twisting the throttle shaft in the carbs (not a good thing... I had to replace one already due to corrosion...it requires drilling the shaft so again..do take care)

    - I had set the initial timing to 17degrees at 900rpm with vacuum advance disabled. I just set it to 15degrees as per Z garage's excellent weber advice. I will play more down the road. Going to 15 seemed to make no significant difference. http://datsunzgarage.com/weber/
    Last edited by Blue; 08-05-2012 at 08:27 PM.
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  21. #21
    Supporting Member Zedyone_kenobi's Avatar
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    Awesome post.

    I have to agree the marriage of the throttle plate and mixture screw is paramount and also convoluted. Both due the same thing. I was able to find a happy idle on my L28, but I want to get the mixture screw back to the magic 1 turn out from fully seated.

    I am currently running 55F8 idle jets. Now it is important to know what those numbers mean. The 55 is the size of the jet, a bigger number is a larger fuel orifice. The last number is the air orifice. This lets in more air. Now this is where it gets tricky. The Fx numbers are not increasing as numbers go up.

    In essence, the idle jet is like a miniature Main/emulsion tube/Air corrector. You have to find out where your engine is most happy, and unfortunately, it will be an expensive task.

    Most expert tuners often fall back on the 'suck it and see' method. There are just too many variables in play to get it right on the first try. But having synchronizes and wide bands give you the information to give you more data with which to make decisions on.

    A 55F9 will run richer than a 55F8. An F8 has a larger air opening than an F9. Go figure. I have the sizes in ascending order in one of my weber books for the DCOE jets. I will post those tonight. Currently I have the first progression hole totally blocked off, and I am about 2.5 turns out from fully seated on my mixture screws. So my idle needle is doing pretty much all the work, and any movement of my throttle plates will uncover the first progression hole.

    If I put my mixture screws about 1 turn out , the car will not run, it dies, and I go crazy lean. According to all the literature I have read, I will need to up the idle circuit.

    I have ordered 50F9 to see where that gets me. I am gambling a bit on reducing the size of my fuel orifice, but I think the smaller air orifice will drive my mixture to the rich side more. I will report back and find out. Getting the idle circuit spot on is so critical as that makes the transition to the mains easier to tune.

    Also, remember to do all your weber tuning with the engine fully up to temp. You do not want to tune for start up. HA
    1971 240Z HLS30-38691
    93.9% done and getting better every day
    Now with 100% more DATSUN SPIRIT L28 Power
    1968 Datsun 2000 SRL311-03416

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    Registered User madkaw's Avatar
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    This is where I'm at on the Mikunis . Too small on the pilots make for a weak transition . If you richen up a small pilot to make transition better, you wind up with a rich idle.
    Pilots are on order
    Steve
    71 240z,bw-5sp 2.4-40 over,balanced,e-88,big valves,ported&polished, stage2,header, triple Mikuni's 40's
    3.90 Subaru STI LSD

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    Registered User LeonV's Avatar
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    Quote Originally Posted by Zedyone_kenobi View Post
    Awesome post.

    I have to agree the marriage of the throttle plate and mixture screw is paramount and also convoluted. Both due the same thing. I was able to find a happy idle on my L28, but I want to get the mixture screw back to the magic 1 turn out from fully seated.

    I am currently running 55F8 idle jets. Now it is important to know what those numbers mean. The 55 is the size of the jet, a bigger number is a larger fuel orifice. The last number is the air orifice. This lets in more air. Now this is where it gets tricky. The Fx numbers are not increasing as numbers go up.

    In essence, the idle jet is like a miniature Main/emulsion tube/Air corrector. You have to find out where your engine is most happy, and unfortunately, it will be an expensive task.

    Most expert tuners often fall back on the 'suck it and see' method. There are just too many variables in play to get it right on the first try. But having synchronizes and wide bands give you the information to give you more data with which to make decisions on.

    A 55F9 will run richer than a 55F8. An F8 has a larger air opening than an F9. Go figure. I have the sizes in ascending order in one of my weber books for the DCOE jets. I will post those tonight. Currently I have the first progression hole totally blocked off, and I am about 2.5 turns out from fully seated on my mixture screws. So my idle needle is doing pretty much all the work, and any movement of my throttle plates will uncover the first progression hole.

    If I put my mixture screws about 1 turn out , the car will not run, it dies, and I go crazy lean. According to all the literature I have read, I will need to up the idle circuit.

    I have ordered 50F9 to see where that gets me. I am gambling a bit on reducing the size of my fuel orifice, but I think the smaller air orifice will drive my mixture to the rich side more. I will report back and find out. Getting the idle circuit spot on is so critical as that makes the transition to the mains easier to tune.

    Also, remember to do all your weber tuning with the engine fully up to temp. You do not want to tune for start up. HA
    Newer Webers (151) have idle mix screws with a finer thread pitch. One turn out on the old carb means more like 2 turns out on the new ones. FYI...

    So being 2.5 turns out on the new ones is comparable to 1.25 turns on the old ones.
    Last edited by LeonV; 08-06-2012 at 10:45 AM.
    2/74 260Z

  24. #24
    Supporting Member Zedyone_kenobi's Avatar
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    That is great information, I had no idea!

    Back to the idle mixture jet information I promised...

    "...In order of ascending size, the air bleed orifice diameters are F6, F13, F9, F8, F2. (F11 has the same size air bleed orifice as F8 but the axial bore is smaller)...

    So an F6 would have the smallest air bleed orifice, and an F2 would have the largest air bleed orifice. Meaning if you keep the fuel orifice fixed(the XX in the XXFy idle jet number) , going from F6 to F2 would make you run much leaner.

    Data taken from the book, "Weber Carburetors tuning tips and techniques", published by Brooklands Books, written by John Passini
    1971 240Z HLS30-38691
    93.9% done and getting better every day
    Now with 100% more DATSUN SPIRIT L28 Power
    1968 Datsun 2000 SRL311-03416

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    Nova Scotia,Canada,Earth Blue's Avatar
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    Well my experience with triple weber 40DCOE151's so far is that I can make them run rich or lean by playing the mixture screw against the throttle plate opening.

    I read the blurb "DCOE INITIAL SETUP & TUNING" in the DCOE chapter in "WEBER CARBURETOR REPAIR AND TUNING BOOK" by Pat Braden. He suggests:

    1. Once engine is warmed up and idling, set all mixture screws at same position out then synchro-balance airflow into all carbs (using throttle valve opening screws and air bypass screws). All 6 should flow the same.

    2. Install air filters and connect tach

    3. Reduce RPM to ~ 900 with the three throttle valve opening screws (for triples).

    4. Turn out all mixture screws to find the point of fastest/smoothest idle. (If no peak RPM is found, repeat step 3 but use 850 or 800 rpm if possible).

    5. Once the maximum RPM point is reached reduce RPM to ~ 900 (or whatever idle RPM you desire) with the three throttle valve opening screws.



    I sort of did this when I first set up the carbs but I was pig rich. Now that I have read a few articles, I will try again... when I get the car back from the "panel tweaker".

    I will also plot idle screw, throttle plate variations, A/F with 1100 rpm constant "for fun"... maybe a graph will talk to me. Especially if I also substitute throttle plate turns in with first pilot hole exposure.
    Last edited by Blue; 08-06-2012 at 07:22 PM.
    There is scarcely anything in the world that some man cannot make a little worse, and sell a little more cheaply.
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    Nova Scotia,Canada,Earth Blue's Avatar
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    This excellent post notes the difference in DCOE mixture screws and provides good advice.
    There is scarcely anything in the world that some man cannot make a little worse, and sell a little more cheaply.
    The person who buys on price alone is this man's lawful prey.


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    Supporting Member Zedyone_kenobi's Avatar
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    Default Tuning weber DCOE 40 on a modified L28

    Okay, I know this is a thread about the L24 that I started, but I thought it would be great to start with one weber setting for say a OEM L24, and trace the tuning required to get the same carbs to run well on a modified L28. Which is exactly what I am trying to do now.

    My current settings are:

    40 DCOE webers
    30mm chokes
    130 main jets
    170 Air correctors
    F11 Emulsion Tube
    55F8

    I forget the accelerator pump sizing, but for now lets not worry about that, as I think if you get the jetting right, the accelerator pumps will be fine over a very wide range.

    My L28 specs are important to this thread as well. As you need to know what I am coming from and what I am going to:

    2.8L N42 block
    N42 head
    .472 lift cam
    10.5:1 compression
    Ross forged pistons
    OEM L28 crank
    OEM L28 rods
    6-2-1 ceramic coated header
    Pertronix igniter and flamethrower coil
    9 lb flywheel
    Standard Cannon Intake manifold

    When I first put the carbs on the new L28 from the L24, I did not so much as adjust anything. I wanted a straight out of the box run.

    Well the L28 would not even start on the original L24 settings. I had to turn the mixture screws over 3.5 complete turns out from fully seated before I got it to idle. Obviously not the best setting. My AFR at that point was about 13:1, and I could get it to 12.5 with some tweaking.

    The engine idled fine and settled down to about 950 - 1000 rpm with ease. Driving at steady state speeds at low rpm in 4th gear you could feel the engine surge just a tad and the AFR's were about 15.9 - 16.5:1. This is way lean for steady state cruise. In 3rd gear the numbers would improve a tad to mid 15's, and in second it would be low 15's, high 14's. All of these values were at low rpm steady state cruise at around 2000 rpm. Giving it gas would bring the numbers back into the 12's but that is probably due to the accelerator pumps fuel input. When we got back to steady state cruise it would be VERY lean again.

    So this afternoon, I started the rejetting process. I got the car started and back up to normal operating temp (which in my case is about 180 Deg). I was still at about 11.9:1 AFR at idle. If I tried to lean it up a bit the engine would slow down.

    So the first thing I changed out was to change the 55F8 idle jet to a 55F9 idle jet. This basically means the fuel orifice was not changed, but the air orifice in the idle jet is smaller. Upon start up, the AFR was immediately 10.9:1. This makes perfect sense. Keep in mind the air corrector acts like a vacuum bleed. Going smaller means the vacuum signal will have more of an effect in pulling fuel up the idle jet. I was able to turn the mixture screws in to get the AFR back to 12.5:1. When I shut the car off, I counted the turns I was out from full lean. Keep in mind with the 55F8's I was 3.5+ turns out. Now with the 55F9's I am 1.75 turns out from full lean.

    Next report will be to see how much effect the idle jets has on my lean steady state low rpm cruise.

    When tuning webers, you must have the engine up to temp, and then only change ONE Thing at a time, and record the results. Write them down in a book or in a web forum (or in my case, both! )

    I will go for a drive tomorrow, and let you guys know what the results are
    Last edited by Zedyone_kenobi; 08-10-2012 at 05:22 PM.
    1971 240Z HLS30-38691
    93.9% done and getting better every day
    Now with 100% more DATSUN SPIRIT L28 Power
    1968 Datsun 2000 SRL311-03416

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    Nova Scotia,Canada,Earth Blue's Avatar
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    Idle Mixture Screw Pitch on 40DCOE2 is 0.8mm

    I'll measure it on the 40DCOE151's when I get close to them(100km away presently)

    The other important part to measure is the taper of the screw. I'll measure that optically.
    Last edited by Blue; 08-14-2012 at 10:26 AM.
    There is scarcely anything in the world that some man cannot make a little worse, and sell a little more cheaply.
    The person who buys on price alone is this man's lawful prey.


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    Supporting Member Zedyone_kenobi's Avatar
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    Default

    I have been meaning to drive around and finally did right before a rain today. I was on vacation and the car had to sit waiting for tuning.
    But the change from the 55F8 to the 55F9 produced a very rich idle and brought the low rpm mixture down from from a lean 15.9 to 16.4 to around mid 15's. I went driving around and noticed aside from having to change my mixture screws up at idle, not much else changed. So I went and installed the 50F9's I had. this was a smaller fuel orifice along with the same size air orifice. Well my 4th gear cruise at 55ish miles per hour is a golden standard I am using. Leaving everything else the same...


    4th gear at 55 mph; which equates to 2500 rpm with very little pedal input.

    55F8 AFR 16.5 - 16.9:1
    50F9 AFR 15.5 - 15.9:1
    55F9 AFR 14.8 - 15.1:1

    The dramatic change in AFR tells me that my main circuit may not be coming in strong yet, as my idle jet seems to be still in the drivers seat.

    The AFR at steady state cruise around 14.8 - 15.1:1 seem okay to me and mean I am around stoichiometric if not a tad on the lean side, but for steady state cruising, at little to no load, this could be a good economy for long trips.

    Now lets us talk about what happens when I give her the beans! Well the AFR plummets. How low. I have seen as low as 10.7:1. This is obviously not what I am looking for, as that is far too rich, and the blurble out of the exhaust when shifting from 1st to 2nd, seems I have some extra fuel in there not burning off.

    I have thought for a while that 130 mains were a bit too rich. I would like to see my AFR drop to 12:5 in WOT conditions, not in the 11's or 10's. I will keep going down jet sizes until I get the mixture where I would like it under WOT.

    This is the only way to tune Webers as far as I can tell. You have to invest in jets and then set up some simple and controlled tests. Write down what you find.

    I am happy with where I am right now on on the idle jet. I would like it be a bit richer though, as it is close to 100 deg F right now and when it gets cold, things will get a bit leaner. I like where I am with the 55F9 idle jet. However, I want to go richer. So would the right thing to do be to order the 60F9 jet, or the 55F13? I honestly do not know. You see the the 60 has a larger fuel orifice, while the F13 has a smaller air bleed orifice. Both will get more fuel into the system, but achieve it differently. Not sure which would be the right one. The easy answer is to buy both. But these get expensive, and I have not found a supplier of F13 idle jets.

    So I used my favorite carb supplier (http://www.carburetion.com) to get some 120 DCOE mains and a 60F9 idle jet.

    I am narrowing down on this tune. I will be darn close with this last order. The principle tuning method of 'suck it and see' is very very true, but I cannot even fathom how hard and how LONG this would take without a wideband O2 sensor.
    Last edited by Zedyone_kenobi; 08-17-2012 at 02:52 PM.
    1971 240Z HLS30-38691
    93.9% done and getting better every day
    Now with 100% more DATSUN SPIRIT L28 Power
    1968 Datsun 2000 SRL311-03416

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    Registered User d240zx2's Avatar
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    The seat of your pants would be worn slap-dad out!
    First & Third owner of HLS30-00721
    B. 01/70 D. 03/12

    New owner of HLS30-15653
    B. 12/70 D.

    Frank in Houston, Texas

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    FWIW, Keith Franck's Hypojets have 4 selectable air-bleeds. This makes it into an adjustable idle jet, 4-in-1.
    2/74 260Z

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    OOOO, I am a Keith Frank believer...Are you using those Leon? If so, how are they?

    Just checked them out..To purchase the hypojets and the hybojet insert it will run you 150 dollars plus shipping. The 28 Hypojet insert is about the same as the 60F9 idle jet I have ordered according to Mr. Franck. I am not sure if the 'improved tunability' of the hypojets would make me want to dump 150 bucks into this setup though. granted I have spent much more than that already , but I have options. If I buy the wrong idle jets, I am out 42 bucks. But if I buy the wrong hypojet inserts, I am out 150 bucks. Well, really just 90 bucks, as I can reuse the hypojet housings. I am tempted to try, as I am a carburetor fanatic just to see the difference.

    Tell you what I am willing to do. I will get the 60F9 idle jet in, and I will see if it is as perfect as I think it is going to be. I will then order the KF setup and give it a try. I would be fascinated to know the difference.


    Here is KF weber store. I see the Emulsion Tube 02 is for 30 mm choked carbs. I wonder how it compares, but at 40 bucks a copy, that is EXPENSIVE
    http://www.webstore.com/82598,owner_id,other_items
    Last edited by Zedyone_kenobi; 08-17-2012 at 05:06 PM.
    1971 240Z HLS30-38691
    93.9% done and getting better every day
    Now with 100% more DATSUN SPIRIT L28 Power
    1968 Datsun 2000 SRL311-03416

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    Registered User LeonV's Avatar
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    Quote Originally Posted by Zedyone_kenobi View Post
    OOOO, I am a Keith Frank believer...Are you using those Leon? If so, how are they?

    Just checked them out..To purchase the hypojets and the hybojet insert it will run you 150 dollars plus shipping. The 28 Hypojet insert is about the same as the 60F9 idle jet I have ordered according to Mr. Franck. I am not sure if the 'improved tunability' of the hypojets would make me want to dump 150 bucks into this setup though. granted I have spent much more than that already , but I have options. If I buy the wrong idle jets, I am out 42 bucks. But if I buy the wrong hypojet inserts, I am out 150 bucks. Well, really just 90 bucks, as I can reuse the hypojet housings. I am tempted to try, as I am a carburetor fanatic just to see the difference.

    Tell you what I am willing to do. I will get the 60F9 idle jet in, and I will see if it is as perfect as I think it is going to be. I will then order the KF setup and give it a try. I would be fascinated to know the difference.


    Here is KF weber store. I see the Emulsion Tube 02 is for 30 mm choked carbs. I wonder how it compares, but at 40 bucks a copy, that is EXPENSIVE
    http://www.webstore.com/82598,owner_id,other_items
    I'll get back to you after I go to Keith's place to play with his new stuff, luckily he's local so we can try a few things without having to ship anything. I've been really busy with my EDIS install lately, but I plan to go to his place in the next few weeks hopefully.
    2/74 260Z

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    Supporting Member Zedyone_kenobi's Avatar
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    The weather is finally clearing up and I had time to get the old gal back on the road. I did install the 60F9 jets AND the 120 mains.
    Low and behold the results were fabulous. Well they were good. My AFR at part throttle cruising in all gears is about 13.5:1, and when I give her the beans, there is no flat spot to be felt. EVER. Going WOT and up in the RPM I am getting about 12.5:1 and it gets more and more rich as RPM climbs, but slowly. I know the 30 mm chokes are going to make her run rich on the top end.

    So for now I am going to order some 115 mains as spares, but drive it exactly like it is. When it gets colder in the fall and winter I should be just fine.

    Right now this is the setup:

    120 Main Jets
    170 Air Corrector
    F11 Emulsion Tube
    60F9 Idle jets

    Car feels like it found 30 more HP in the mid RPM band now that it is not so rich, and the pull up above 3000 feels just spectacular. Still I cannot really wring it out because the engine is so new, so I intend to put a hundred miles on her tomorrow weather permitting.

    Last edited by Zedyone_kenobi; 08-24-2012 at 04:36 PM.
    1971 240Z HLS30-38691
    93.9% done and getting better every day
    Now with 100% more DATSUN SPIRIT L28 Power
    1968 Datsun 2000 SRL311-03416

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    Excellent exploratory work! I am happy for you.

    I get to see my 71 resto tomorrow and play.

    Philip
    There is scarcely anything in the world that some man cannot make a little worse, and sell a little more cheaply.
    The person who buys on price alone is this man's lawful prey.


    John Ruskin (1819 - 1900)



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    Quote Originally Posted by Zedyone_kenobi View Post
    Going WOT and up in the RPM I am getting about 12.5:1 and it gets more and more rich as RPM climbs, but slowly. I know the 30 mm chokes are going to make her run rich on the top end.

    So for now I am going to order some 115 mains as spares, but drive it exactly like it is. When it gets colder in the fall and winter I should be just fine.

    Right now this is the setup:

    120 Main Jets
    170 Air Corrector
    F11 Emulsion Tube
    60F9 Idle jets

    Car feels like it found 30 more HP in the mid RPM band now that it is not so rich, and the pull up above 3000 feels just spectacular. Still I cannot really wring it out because the engine is so new, so I intend to put a hundred miles on her tomorrow weather permitting.
    You may want to try out a 190 air corrector to see if it counteracts the richening trend at the higher revs.
    Dave C, Putnam, NY
    NYZCC - Membership Director

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    Quote Originally Posted by cygnusx1 View Post
    You may want to try out a 190 air corrector to see if it counteracts the richening trend at the higher revs.
    The air corrector should not be used to correct upper rpm mixture, that is primarily the main jet's job. Enlarging the air corrector will affect the transition to the mains (larger AC makes mains come in later, increased potential for flat spot). The AFR curve at WOT is controlled by the emulsion tube/main choke combo. The "right" combo will yield a flat curve.
    2/74 260Z

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    Supporting Member Zedyone_kenobi's Avatar
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    I think the main culprit of it richening is the 30mm chokes. I am going to invest in some 32mm to see how they feel. I mentioned above about getting some of the Keith Franck E tubes, but for the money I think 32mm chokes are a better investment. The F11 Etube just seems to be a great fit to Lseries engines.
    1971 240Z HLS30-38691
    93.9% done and getting better every day
    Now with 100% more DATSUN SPIRIT L28 Power
    1968 Datsun 2000 SRL311-03416

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    Without swapping emulsion tubes, and no flat spots apparent in your setup, the air corrector can take out some high-rev fuel. Not correct, but it works to some extent. I went from 28 to 32 mm chokes in my 151's. It's worth doing. I didn't also change the aux venturis to be "by the book" but it runs fine.
    Last edited by cygnusx1; 08-27-2012 at 05:50 PM.
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    Can I change out the venturies with the carbs still on the car? It looks like they just pull out.
    1971 240Z HLS30-38691
    93.9% done and getting better every day
    Now with 100% more DATSUN SPIRIT L28 Power
    1968 Datsun 2000 SRL311-03416

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    Yes, with the vel. stacks off, they should slide out with little effort.
    Last edited by cygnusx1; 08-27-2012 at 07:59 PM.
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    Perhaps I can add to the body of knowledge being assembled here. I am in Reno Nevada at 4500ft above sea-level. Ambient in August is a balmy 90+ degrees with 20% humidity. I was running extremely rich this spring when I got her running. (I just moved here). The following was my set up:

    Idle jet 50F9
    E-tube F11
    Main jet 145
    Air correction 170
    Fuel pressure 2psi at idle
    Brass floats set to 5.5
    Mixture screws were 2 turns out

    It ran pretty well with this set-up. But I do have an Innovate LM set up installed in the original ashtray so I can hide it when I want. I would start up and idle at 9.5:1 and pretty much never got much better than 13:1. I made the following changes and took it for a little cruise in the night air just a bit ago. It feels better but I imagine I will need to do some daytime testing and let her get warmed up to tell for sure.

    Idle jet 50F8
    E-tube F11 (stayed the same)
    Main jet 140
    Air correction 180
    Fuel pressure 2psi at idle (stayed the same)
    Brass floats set to 8
    Mixture screws 1.5 turns out
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    Rob
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    1973 Datsun 240Z Restoration project. New paint in original white. E31 head on 2.4 block. Nissan Motorsports header. R200 with Nissan motorsports LSD.

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    Very nice install!

    That 50F8 idle jet should really lean you out ! It was almost 2 points leaner than my 55F9 jets
    1971 240Z HLS30-38691
    93.9% done and getting better every day
    Now with 100% more DATSUN SPIRIT L28 Power
    1968 Datsun 2000 SRL311-03416

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    I should mention, my carbs are 42 DCOE 8 triples not 40's. After a little drive this morning I find that I have developed a flat spot on tip in, especially aggressive tip in. But, my A:F numbers are much improved. It idles in the 11:1 range and except for when I drop the throttle, it stays in the 12 and 13:1 range. Drop throttle gets you 15:1 and there about... I have found some throttle response and power that wasn't there before which is really nice. Now, how to deal with the flat spot?

    Thanks for the props on the install.
    Last edited by conedodger; 08-28-2012 at 09:04 AM.
    Rob
    2000 BMW R1100 RT-SE (for sale)
    1999 Toyota 4Runner Supercharged
    1975 Porsche 914 stroker motor autoX car
    1973 Datsun 240Z Restoration project. New paint in original white. E31 head on 2.4 block. Nissan Motorsports header. R200 with Nissan motorsports LSD.

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    Quote Originally Posted by conedodger View Post
    I should mention, my carbs are 42 DCOE 8 triples not 40's. After a little drive this morning I find that I have developed a flat spot on tip in, especially aggressive tip in. But, my A:F numbers are much improved. It idles in the 11:1 range and except for when I drop the throttle, it stays in the 12 and 13:1 range. Drop throttle gets you 15:1 and there about... I have found some throttle response and power that wasn't there before which is really nice. Now, how to deal with the flat spot?

    Thanks for the props on the install.

    For flat spot:

    1. Set fuel surface from the top of the casting ledge of the main jet well.
    2. Play with bleed back hole size and accel pump length if you lean-out on punching it. (Old racers say to "squeeze" the pedal rather than punch it...I am thinking they ran Webers that were not transitioning well.)
    There is scarcely anything in the world that some man cannot make a little worse, and sell a little more cheaply.
    The person who buys on price alone is this man's lawful prey.


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    Supporting Member Zedyone_kenobi's Avatar
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    I would also go down one size on your air corrector. It may help with the flat spot.
    well it worked for me!
    1971 240Z HLS30-38691
    93.9% done and getting better every day
    Now with 100% more DATSUN SPIRIT L28 Power
    1968 Datsun 2000 SRL311-03416

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    Quote Originally Posted by Zedyone_kenobi View Post
    I would also go down one size on your air corrector. It may help with the flat spot.
    well it worked for me!
    I just ordered the Franck fuel level tool. I will set my fuel level with that first. I believe he says 25mm is ideal? I can't wait to see how this thing works.
    Rob
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    Quote Originally Posted by conedodger View Post
    I just ordered the Franck fuel level tool. I will set my fuel level with that first. I believe he says 25mm is ideal? I can't wait to see how this thing works.
    It's a great tool, but might take a little practice to use. Dip it in and out of the fuel a few times and look inside the center of the PC tube. You'll get the hang of it quickly, it's an awesome tool!
    2/74 260Z

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    My head hurts to read this, too much technical data All i wanna know is how big performance boost do you get with triples? :P
    -72 240Z "Goldie"

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    Quote Originally Posted by Koalia View Post
    My head hurts to read this, too much technical data All i wanna know is how big performance boost do you get with triples? :P

    I noticed crazy low rpm torque boost. It is nice to see a 2nd opinion with the same finding here...and data: http://datsunzgarage.com/weber/
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    I followed a link posted here and ended up on Sidedraft.org or some such site. I joined and posted and Keith Franck himself has offered to meet me at Thunderhill and tune my carbs! He says if the tune is right, density altitude will not make much difference...
    Rob
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    1975 Porsche 914 stroker motor autoX car
    1973 Datsun 240Z Restoration project. New paint in original white. E31 head on 2.4 block. Nissan Motorsports header. R200 with Nissan motorsports LSD.

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    Quote Originally Posted by Blue View Post
    I noticed crazy low rpm torque boost. It is nice to see a 2nd opinion with the same finding here...and data: http://datsunzgarage.com/weber/
    I noticed the same thing. I can take off from a standstill in 2nd gear, as if it's first.

    Quote Originally Posted by conedodger View Post
    I followed a link posted here and ended up on Sidedraft.org or some such site. I joined and posted and Keith Franck himself has offered to meet me at Thunderhill and tune my carbs! He says if the tune is right, density altitude will not make much difference...
    Nice! I should hopefully be meeting with Keith next week.
    2/74 260Z

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    OOPS double post



    I know I'm not a Weber guy, but I will agree with the great gain in lower end. Of course this is probably subject to the cam each of us are running. With my Mikuni's I kept pushing the envelope of the pilot side by seeing how rich I could get it. When I thought I was putting too much emphasis on the pilots and tried making corrections elsewhere, I would still be fighting the 'dead spot'. I started with 200 main airs and ended up with 180's. Started with 57.5 pilots and ended up with 67.5's. Had 40's acc.pumps and went back to 47's.
    In MY CASE, my motor wanted it down low. My engine pulls hard right from 1500rpm straight thru to 6000rpm. Only on a dyno will I know for sure what the number look like.
    I am idling anywhere from 12 to 13, and cruise is around 14 AFR. As I have read before, they like to run rich. Thus the advantage of EFI, nice lean idle and cruise, then dial in the power zone. Makes me want ITB's even more.
    Last edited by madkaw; 08-31-2012 at 03:47 PM.
    Steve
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    Default Mikuni guy weighing in!

    I know I'm not a Weber guy, but I will agree with the great gain in lower end. Of course this is probably subject to the cam each of us are running. With my Mikuni's I kept pushing the envelope of the pilot side by seeing how rich I could get it. When I thought I was putting too much emphasis on the pilots and tried making corrections elsewhere, I would still be fighting the 'dead spot'. I started with 200 main airs and ended up with 180's. Started with 57.5 pilots and ended up with 67.5's. Had 40's acc.pumps and went back to 47's.
    In MY CASE, my motor wanted it down low. My engine pulls hard right from 1500rpm straight thru to 6000rpm. Only on a dyno will I know for sure what the number look like.
    I am idling anywhere from 12 to 13, and cruise is around 14 AFR. As I have read before, they like to run rich. Thus the advantage of EFI, nice lean idle and cruise, then dial in the power zone. Makes me want ITB's even more.
    Steve
    71 240z,bw-5sp 2.4-40 over,balanced,e-88,big valves,ported&polished, stage2,header, triple Mikuni's 40's
    3.90 Subaru STI LSD

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    But it is a great double post!
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    Formerly known as Koalia Reverend's Avatar
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    How have you guys accomplished the positive crankcase ventilating? I read from the link Blue gave that there is no pvc inlet in triples. Someone might have wrote about it in this thread, but my eyes go crossed when trying to find it in the middle of technical jungle.
    Last edited by Reverend; 09-05-2012 at 01:33 AM.
    -72 240Z "Goldie"

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    I am not sure if this counts but I once tapped into the filter boxes to vent my Alfa crankcase back into the carbs.
    Dave C, Putnam, NY
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    Quote Originally Posted by Koalia View Post
    How have you guys accomplished the positive crankcase ventilating? I read from the link Blue gave that there is no pvc inlet in triples. Someone might have wrote about it in this thread, but my eyes go crossed when trying to find it in the middle of technical jungle.

    Check this one: http://what-when-how.com/automobile/...ol-automobile/
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    Quote Originally Posted by Koalia View Post
    How have you guys accomplished the positive crankcase ventilating? I read from the link Blue gave that there is no pvc inlet in triples. Someone might have wrote about it in this thread, but my eyes go crossed when trying to find it in the middle of technical jungle.
    http://www.zcar.com/70-83_tech_discu..._686437.0.html
    2/74 260Z

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    We last left our hero with a very functional setup of the following:

    120 Main Jets
    170 Air Corrector
    F11 Emulsion Tube
    60F9 Idle jets

    This yielded a decently smooth idle and a steady state cruise AFR of around 12.9:1.
    Going to lunch the other day though, my friend who was following me told me that I was reeking of gas behind the car. This concerned me. Needlessly running rich does not yield any advantages at all.

    so lets try to figure out what was happening. First at around 2600 rpm in 4th, the throttle plates are barely cracked. I think it is very safe to say I am NOT pulling form the main circuit at this time. So it has to be in the idle jet. The more I thought about this, the more clear it seemed. Simple tests for idle jet 'correctness' at least from an AFR point of view.

    When I was idling at 12.5:1 the mixture screws were barely 1.5 turns out. As Blue noted and I confirmed through more reading, the 151's really need more than this. More like 2 full turns. But I will get back to that.

    Keeping in mind the mixture screw does not adjust Air/Fuel mixture. It is merely an opening that allows premixed air and fuel to enter the throat of the carb. The more you open it, the more premixed air and fuel enters. This means that you can get the car to idle with darn near any idle jet by making adjustments to the idle screws to get enough fuel in there. I would wager that there are limits to this, but for the most part if you are close you can get her to idle. So how do you know if you are crazy rich on the idle jet?

    My moment of clarity came as I was taking a long tuning drive down the freeway. Any tip in I did in 4th gear at around 60 mph I immediately dropped to 10:1 AFR. If I kept my foot more in it (meaning I introduced the main circuit into the equation), my AFR got closer to 13:1.

    So my webers were talking to me and I was not listening!! What do I mean? Well since I had to go so far down on my mixture screws to get my idle AFR in a happy place (deemed as 12.5:1 by popular opinion) and my AFR while solely in the progression circuit (which is also fed by the idle jet) was dipping in to the 10's it tells me that the premixed air/fuel from the 60F9's was too rich! Now post #34 seems to contradict this, but looking back at my hand written notes, I made that assumption too quickly. I did not take her on the freeway long enough or do a long enough drive. I think I was getting into the main circuit when I stated that my part throttle AFR were spot on. When I carefully drove on the free way at very slight openings of the throttle, the AFR is indeed in the 10's.

    My biggest problem is that I never have enough time to do more than one test per week. I need more time to test and document these things. GRRRR.

    my quickie fix was to remove the 60F9 and install the 50F9's. I was able to adjust the mixture screws 2.25 turns from fully seated, when I attained the 12.5:1 AFR at 1000 rpm. Also of note, my idle did get smoother and the AFR reading was not as bouncy.

    I may still need to install the 55F9s. We will see. But all of this will be thrown out the window as I have ordered my 32mm chokes from www.carbsunlimited.com. So we will have to tweak these all over again at a later date.

    If you wonder if I am having fun messing around with these. Well the answer is a resounding yes!!! I love carburetors. I love the fact that it requires a certain skill set to make them work correctly. I love the trial and error portion of the work.
    1971 240Z HLS30-38691
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    Now with 100% more DATSUN SPIRIT L28 Power
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    Default DCOE Idle Circuit Clarity

    Stephen, I think you are going in the right direction. New chokes will change things in the upper end for sure... not sure about idle as the air flow is too low for the choke to affect anything...probably during progression that you will see a change. I read a huge post on HybridZ on DCOE configurations but most of it is useless as there is very little useful reference data coupled with a possible "hillbilly" element.I figured the "Use a configuration that someone else took a lot of time and energy and money to achieve" would be the way to go but when the fuel level or initial timing or idle throttle plate opening, or # of turns out on the enrichment screw for someone's "perfect setup for XXX engine" is not disclosed,who knows if they set it right or their set-up is fixing a problem they caused. For me, the only way forward is to do it scientifically and try to control/understand the variables.Here is a start for the idle circuit and the inter-relationships of the parts.Here is a crude drawing I made to represent the variables:
    I did notice that I could play the Idle Enrichment against the Throttle Valve stop screw to get a variety of A/F ratios so here is what I think is going on along with unknowns:Idle Circuit Interworking Analysis "Talk-Through":

    1. Fuel level 25mm below shoulder of main jet.

    2. Timing >=15 degrees at 900 RPM

    3. Throttle Valve stop screw 1/4 turn in from the plate resting in the throat (this is to prevent wear on the plate and throat and only allows a wee bit of air into the motor). Assume all linkage and throttle plates are set correctly and all 6 work the same. In theory this should be completely closed so that all air is from the idle needle port however it can not be completely stopped due to throttle-plate-to-throat wear.

    4. Idle enrichment screw. This allows air and fuel mix into the motor. High manifold vacuum "sucks" both air and fuel out of the small hole below the screw. The amount drawn is dependent on manifold vacuum and the number of turns on screw and the taper of the screw's needle. (pitch of the screw thread is the same for most if not all DCOE carbs).

    Gotta go to lunch. More later.
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    Last edited by Blue; 07-29-2014 at 04:54 AM.
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    Zed, in short, you discovered, like I did, that the idle jet size IS your progression mixture, not really your idle mixture. Those Italians, I'll tell you!#! 32mm chokes will have nil effect on your idle, and nil+1 effect on progression. I like the 55F9 that I just put in. I think that's a good idle jet for the 151's on my L28.

    Expect your mains to go up to 135 or so, and maybe up the air corrector to match. Got a micro drill set and a soldering torch yet? I make my own jets.

    Oh BTW, my Webers talk to me too. You are not alone.
    Last edited by cygnusx1; 09-12-2012 at 08:34 AM.
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    I fully expect my mains and airs to go up with the 32's. I think I will end up with the 55's.
    I am glad to hear the 32mm will have zero effect on my idle and progression. As they are very nice right now!

    I do not have a micro drill, but I do have a nice soldering torch... man you are an enabler!
    1971 240Z HLS30-38691
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    Now with 100% more DATSUN SPIRIT L28 Power
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    4 (continued). The progression holes upstream from the idle enrichment needle valve also allow air to mix with the enriched fuel from the idle jet.

    5. Depending on the location of the top of the throttle plate relative to the first progression hole:

    i. If the plate is far from the first progression hole and inboard towards the block,the progression holes will only add air to the idle mix (assumption)

    ii. If the plate is very near the first progression hole, the first progression hole may draw fuel and air from the idle jet due to the venturi effect at the throttle plate. This may decrease the flow out of the idle port or it may have minimal effect on the idle port's flow (unknown). Of course there will be more air past the throttle plate that dilutes the fuel mix.

    iii. If the plate is under the first progression hole, the first progression hole may draw additional fuel and air from the idle jet due to the venturi effect at the throttle plate and from more exposure to manifold vacuum.(assumption) This may decrease the flow out of the idle port or it may have minimal effect on the idle port's flow (unknown). Of course there will be more air past the throttle plate that dilutes the fuel mix.

    iv. If the plate is past the first progression hole, the first progression hole may draw fuel and air from the idle jet due to the venturi effect at the throttle plate and from more exposure to manifold vacuum.(assumption) This should decrease the flow out of the idle port however the combined flow out of the idle port and the well exposed first progression hole may flow more fuel or less fuel. (unknown) Of course there will be more air past the throttle plate that dilutes the fuel mix.

    From the above, as the the throttle valve is opened more and the idle enrichment screw is correspondingly closed, the idle mix will become weaker AND the idle enrichment screw somewhat balances how much fuel is pulled from the idle port vs the progression holes (i.e. taken to the extreme, a huge 2mm idle jet fuel hole will cause fuel to pour into the progression holes but the idle enrichment screw can completely block any fuel from reaching the idle port....thus the balance effect)

    It is clear that as the throttle valve is opened, the idle port's flow will decrease thus the idle jet will certainly affect the progression enrichment thus there is an important transitional relationship between idle and progression that must be addressed by idle jet selection.

    As the throttle valve opens further, the main circuit will come in. From experiments, the fuel level in the bowl will affect when the main circuit comes in. When the fuel level is high, the main will come in earlier and reduce the amount of time during progression.


    My intuitive recommendation for tuning the idle and progression is:

    1. Keep the throttle plate as closed as much as possible.
    2. Assuming timing, linkage, fuel level, mains, air flow, valves, etc are all correct, turn out the idle enrichment screws until smooth 900 rpm idle is reached. Adjust throttle plates minimally to achieve 900 rpm.
    3. Measure idle A/F
    4. Drive and measure A/F at low rpms and plot the transition to mains.
    5. If too rich or too lean at idle and progression the switch idle jets and repeat.
    6. If rich at idle and lean at progression then open throttle plate more and turn idle enrichment screw in to have more fuel pulled from the progression holes. (The acceleration pump bleed back and related piston/throw can also be given attention)
    7. If lean at idle and rich at progression then close throttle plate more and turn idle enrichment screw out to have more fuel pulled from the idle hole. (The acceleration pump bleed back and related piston/throw can also be given attention)
    Last edited by Blue; 09-12-2012 at 10:54 AM.
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    Default Leaking Acceleration Circuit

    Something interesting from this site: http://www.webercarburatori.com/?p=handbook&s=2


    The main features of accelerating pump operation are the amount of fuel injected at each stroke and the promptness and duration of each injection. When tuning up for proper adjustment settings, the pump jet and drain diameters are determined by trying to minimise, as far as practicable, the amount of fuel injected. Often, also the direction of the fuel spray proves to be a significant factor. Generally, when engine operates at high rpm rates the pump jet (diameter between 0.35 and 1 mm) is subject to a vacuum sufficient to produce an uninterrupted flow of fuel, that is, it performs as a high speed jet and its role falls under the adjustment setting data.


    I had brought this up to Keith Frank on his forum when I saw it in data and another forum member did a few additional runs to verify what I saw (a "leaky accelerator circuit"). I even suggested turning the jet nozzle around. Now it is documented in a Weber manual so I am happy

    My solution for a Weber mod was to put small springs rather than weights over the ball valves as vibration and mass cause the balls and weights to jiggle and bounce and not seal effectively. A spring would not do this and keep the ball down until fluid pressure was applied by the plunger.


    Eureka! A video to prove it! Not a DCOE but the same principal:

    Look at the leaky accel jet spraying at the Philips screw head. I saw this on a graph nearly a year ago... now I see the theoretical! That's a Higgs Boson to me.

    Last edited by Blue; 09-12-2012 at 12:39 PM.
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    Registered User LeonV's Avatar
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    That's a great video!
    2/74 260Z

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    That is a holley carb if I am not mistaken.
    1971 240Z HLS30-38691
    93.9% done and getting better every day
    Now with 100% more DATSUN SPIRIT L28 Power
    1968 Datsun 2000 SRL311-03416

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    Default

    I read your posts and I don't understand why you rely on AFR at idle. I always setup idle at best lean condition then play with idle screw to set the idle speed correctly.
    I also was having issue with unproper idle jets but change in size fixed everything on my case (I'm having DCOE 18, maybe that's why)
    AFR at 2500rpm cruising has always been around 14:1 / 14.5:1 this way.
    I'm measuring AFR with a clamp at exhaust tip so it makes even less sense to bother but would it be crazy to believe you might have reversal flow even close to the engine because of engine low operation? That could lead to false reading.

    So to come back to idle adjustment, idle is always ok once set - whatever the idle mixture screw settings are - but good progression needs to have proper jets. It appears progression is almost always perfect when I'm near 1.5 turn from fully closed with the proper idle jets (50f9 with previous skock N42 head on L28 & now 45f9 on modified P79 head). So in my particular case, I'm just experiencing what the weber books are stating.
    I also check plugs after some gentle sessions, Comparing plugs allows me to fine tune AFR balance also.

    Regarding sealing of the throttle plates at idle, I observed they are not really sealing fully the bore.
    I've adjusted & sync'ed my carbs while they were all on a bench; I was looking thru them while closed with a light behind. You can then clearly see the light spreading around the throttle plate allowing me to get similar pattern accross carbs.
    BTW, this method did not bring any good result to me (so don't waste your time )

    Regarding accel jet leakage at WOT, should we be worried? if it is repeatable, we should just take them into consideration while tuning, shouldn't we?

    Last comment, I've also checked the bleed jet at the bottom of my bowls, they are sealed to avoid any bleeding operation with solder & I've got great response from my engine at tip in (with some limits though such as super quick tip in at 1500rpm in 2nd gear). Maybe that's something to investigate as well on your side if you have issue while accelerating.

    I love webers for the same reasons as yours but ultimately, the most enjoyable moment is the reward to have a car running great or making progress
    They never let me down so it helps also since I've never been frustrated with them.
    Last edited by Lazeum; 09-12-2012 at 02:33 PM.

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    So Blue, that would mean you are Blue280ZBlue on the Franck forum... I have followed your travails.
    Rob
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    1999 Toyota 4Runner Supercharged
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    Yeah I got off it a while ago because interesting exploration was mostly by one or two chaps and often poo-pooed by another if their findings were not within his personal limits. Some great data in the archives there.

    I just jumped in today for a much delighted "told you so...and so did the data from last year". That forum has so much potential.
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    Quote Originally Posted by Lazeum View Post
    I read your posts and I don't understand why you rely on AFR at idle. I always setup idle at best lean condition then play with idle screw to set the idle speed correctly.

    Snip
    So to come back to idle adjustment, idle is always ok once set - whatever the idle mixture screw settings are - but good progression needs to have proper jets. It appears progression is almost always perfect when I'm near 1.5 turn from fully closed with the proper idle jets (50f9 with previous skock N42 head on L28 & now 45f9 on modified P79 head). So in my particular case, I'm just experiencing what the weber books are stating.
    Snip

    Hi Lazeum,

    The point I was making is that a/f at idle and progression depend on where you initially set the throttle plate AND covering /revealing the first progression hole. I am not sure what is ideal. In my case, I can set 900rpm idle with little idle enrichment and run lean at cruise or set 900 rpm with lots of idle enrichment and run rich a cruise, all with the same 55F11 idle jet. There is important interplay between the two screws. As well, my transition to mains is not very different in both cases as the fuel level is high at 25mm down and the mains comes in quickly.

    I have more experiments to do but plotting a/f against initial throttle plate position is one that I look forward to measuring.

    Yes you are correct, the acceleration nozzle can be part of WOT tuning. Here is a plot of its effect. The second plot has the accel/ circuit completely blocked and out of service.

    Attached Thumbnails Attached Thumbnails Click image for larger version. 

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    Last edited by Blue; 07-29-2014 at 05:06 AM.
    There is scarcely anything in the world that some man cannot make a little worse, and sell a little more cheaply.
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    your curves are very interesting, I wouldn't have guessed such a difference between the 2 cases. The change seems to have translated the whole curve up by 1 to 2 AFR points, that's a lot!
    If it is a WOT trial, isn't AFR level too high?

    I'm also wondering what could be the reason for the rich spot at 20s on the leaking trial. It does not exist on the second run so I would imagine it could come from accel circuit.
    I can see as well that despite your mains coming early you have a lean spot in between 2500 & 3000 rpm, would it be the progression circuit being out too early? hence the importance of progression port back to throttle plate position you're talking about.
    If you have read the post on webers on HBZ, maybe you've seen my AFR results (p13-15 if I recall), I'd got a rich spot at 4000/4500 rpm for some reason I cannot really explain besides engine dynamic... it appears this rich spot has disappeared with my new head.

    how do you measure AFR also? with a copper pipe used as a sniffer or with a bung welded around the transmission area?

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    The plots are from a nice guy on the yahoo side draft forum.

    I have a theory about the rich spot at ~2,200 rpm too. It is because the top of the throttle plate pinches off with a thick choke next to the accel. nozzle promoting more flow. The accel pump will always open and push as the throttle is pressed and vacuum at this pinched spot will pull more fuel for a moment of transitition.

    I was banned from HybridZ so I will never join...even if I wasn't banned... some useful info there but the admin are "weenies"

    I am sniffing at the tail pipe like you. The copper pipe I made is 600mm long to get a better sniff at idle as it goes deep into the exhaust system.
    There is scarcely anything in the world that some man cannot make a little worse, and sell a little more cheaply.
    The person who buys on price alone is this man's lawful prey.


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    Quote Originally Posted by Lazeum View Post
    snip I always setup idle at best lean condition then play with idle screw to set the idle speed correctly.
    snip

    THANKS! I have been thinking more about your words and it suddenly occurred to me that the idle and the progression do interact however tuning at idle seems illogical as the car must be tuned to run, not to idle AND because the idle enrichment screw can fudge things.

    I think tuning by addressing the progression and cruise first is the best way to start. Fudging air/fuel mix with the enrichment screw at idle and throttle plate is sort of backwards because at cruise, the idle jet should not be significantly feeding the motor. In theory at cruise, the jet and the progression holes AND the throttle plate are the only significant components and the throttle plate will fall where it naturally does to provide x amount of air at cruise.... so by cruising, one can alter the jets to get the right a/f mix then go after the idle.

    In fact it would be interesting to try to tune with the enrichment screws closed completely and just use the throttle plate opening to pull from the first prog hole. If the car will idle like this then a quick cruise with A/F monitoring will tell whether the idle jet is too rich or lean.
    Last edited by Blue; 07-29-2014 at 05:12 AM.
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    just to make sure, when I was referring to "idle screw", I was talking about the screws used to balance the carbs & RPM at idle, not the ones used to play with AFR.
    Matt - 72' 240z

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    Yes I understand. In fact just last night I read a section from "How to Build & Power Tune Weber & Dellorto DCOE & DHLA Carburettors" (SpeedPro Series) by Des Hammill. The section on choosing and tuning idle jets is exactly what I concluded above... convergence is a good thing. Basically he says to choose jets for cruise at progression and for power transitions through progression then address the idle.

    I'll post some of my internet vacuuming finds in a new post.
    Last edited by Blue; 07-29-2014 at 05:14 AM.
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    Today I changed out my 30mm chokes for 32mm chokes. As you would expect not much has changed as far as idle quality, but having said that. For the first time, I was able to get the carbs perfectly balanced at 1000 rpm dead on. All 6 cylinders were pulling identical amounts of air, and also, my AFR was as close to steady as it has ever been. I could get a decent idle before, but it would fluctuate from 12.3 to 13.4, and would cycle seemingly randomly around there, but average about 12.7. Now I do not vary more than .4 on my AFR. I stay about 12.9 to 13.4. My part throttle seems smoother, and it picks up revs very quickly. I cannot wait to drive it to see how she feels.

    But for now, I have the car on jack stands with the front spook off, I am waiting for my ducted spook..
    1971 240Z HLS30-38691
    93.9% done and getting better every day
    Now with 100% more DATSUN SPIRIT L28 Power
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    try 20 degree initial timing and see if you idle smooths out you may have to retard more at heavy load/wot but it made a big difference for my tuning yesterday
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    negative. If run more than 13 I get some pinging at heavy load in 3rd and 4th gear. With 10.5:1 compression that was going to be a risk I was taking. AT 10 degrees advance, I get none. Car seems to run fine. I will try to bump up the octane and run about 14-17 to see how she likes it. I know webers like lots of initial advance. If I can ever get my mallory unilte to work without blowing the ignition module I will order the curve kit for it so I can run more advance initially.
    1971 240Z HLS30-38691
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    Now with 100% more DATSUN SPIRIT L28 Power
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    To tune timing at idle, I start the engine (while already hot) with distributor loose so I can turn it by hand. Turn it and hear the difference from the engine, the rpm will increase or decrease. Best timing will be when the idle will be the highest. This is where you should setup your timing.

    Check with a light where you stand and record the value.

    Do a quick math to determine your dizzy advance based on targeted total advance wanted. With a Mallory Unilite, you can set up this advance. You don't need specific tools (even if it would be nice to get). To offset properly the dizzy, I measure the arc length vs. the radius from where I do the measurement. then I use drill bits with corrrect diameter as a gage for proper adjustment of the 2 plates inside.
    Matt - 72' 240z

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    That's a good idea
    Never even thought about modifying it myself. That definitely easy to do
    1971 240Z HLS30-38691
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    Now with 100% more DATSUN SPIRIT L28 Power
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    Default 30mm vs 32mm chokes on 40 DCOE 151 webers

    Well I took the Z out for a drive with its new 32mm chokes. I made all the appropriate jet changes to come to this configuration:

    130 main Up from 120 main
    180 air corr Up from 170 Air corr
    55F9 idle Up from 50F9

    My first impression was that there was no change. It still idled as smooth as it ever had (no small part to finally getting the air flow through them perfectly balanced). With the 55F9 idle jets, I get 13.9 to 14.7 AFR on steady state cruise at about 60 mph. Even better when I tip into the throttle the AFR drops to only about 12.8 or so. Very nice. At wide open throttle the power improvement is not trivial. It just seems to have more legs up top. It pulls with more authority.

    So all would seem to be well. But is it? The answer is mostly, yes, and a little no. As one might have expect the throttle response is NOT nearly as sharp as with the 30mm chokes. 32mm is definitely on the ragged edge of what I would want to have in a street car. Not that it feels sluggish, or laggy. It does not. It response to all the inputs I give it in the gas pedal. But not nearly as sharply as before.

    The engine with the 30mm chokes seemed to want more air all the time. So any opening of the throttle plate made the engine just respond like getting a breath of fresh air after surfacing from the water after a long dive.

    The engine seems more relaxed with the 32mm, it idles better (not sure chokes should make a hill of beans at idle though), and the ferocity of the upper rpm is notable.

    So long story, for a street car 30mm chokes will work fine on a L28, and give you immediate throttle response that makes a car VERY fun to drive on the back roads. But for a car with deeper lungs, the 32mm are the ticket. If you track your car and live in the higher rpm, I can completely recommend 32mm chokes maybe even bigger.

    My cliff notes is that going to 32mm chokes is not a holy grail of modifications to webers. There is a downside. The magnitude of that down side depends on your personal preference and what you value.
    1971 240Z HLS30-38691
    93.9% done and getting better every day
    Now with 100% more DATSUN SPIRIT L28 Power
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    Great report! What was your AFR at 4k and at 6k?


    Last weekend when I measured and recorded A/F as my brother drove, his driving commentary matched the A/F ratios I recorded: Going with bigger idle jets and lower AFR made the car "sluggish"...similar to your commentary above wrt 32 vs 30mm.

    I am wondering if you can play with mains and air with 32mm chokes to see what happens on each side of 13AFR between 4k and 6k. (120f & 180a vs 130f and 170a)
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    OH blue, thanks for reminding me.

    I meant to include that the 180 Air Corrector reintroduced the slight lag in between the progression circuit and the primary circuit. This happened with the 30mm chokes as well. When I went down to the 170 Air corrector with the 30mm chokes it was gone. I tried the 180 Air corrector on my L24 as well before the engine swap and I had a noticeable flat spot between the two circuits. The 170 air corrector fixed that there too.

    I wanted to give them a try again with the bigger chokes, but the transition stumble was back. I have installed the 170 air corrector again, and I will see what the AFR is at 4 and 6. I have hard time getting 6k rpm 3rd gear runs,as that is really darn fast on public roads! But I will see what I can get you Blue.

    Hopefully those 120 mains will be on your doorstep this week or early next week . I kind of wish I had 125 mains. I feel another order of jets coming on.
    1971 240Z HLS30-38691
    93.9% done and getting better every day
    Now with 100% more DATSUN SPIRIT L28 Power
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    ... I will have 125's freed up once I get the 120's so hang tight.... it sounds like symbiosis.

    I read that more air corr. does move the main's rpm start point out. Good to see it happen in your experiments. I think the only way to counter balance is with etube changes and fuel levels...but at 25mm down in the well, the fuel won't come on any earlier without overflowing the bowl...so e-tube is your only trick left.


    I also read that a rule of thumb is 0.50mm between Fuel and air.... I also read 0.6mm too lol. So for 125fuel you will need 175 to 185 air. The 180 may be worth re-trying with the 125's.



    Check your AFR holding at 4000 to see if you have too much or too little fuel jet.

    Check your AFR holding at 6000 to see if you have too much or too little air corr. (get an assistant for this in third or do it in 2nd on a long gentle hill)
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    I have not done the runs yet Blue, but I have been doing ALOT of driving. I have not totally eliminated my stumble at transition, but gosh it is close to being gone. I have ordred some larger pump jets though as a trial (expensive trial since they are 10 bucks each! OUCH). I want to get more fuel into the car faster. I noticed that the current jet and spring combination the fuel continues to come out from the accelerator pump for a time after the throttle plates go wide open.

    When I had the carbs off to install the 32mm chokes, I had to empty the fuel bowls. Well just tilting the carbs do not work on webers like they do no holleys so I just activated the Accelrator pumps via the throttle shaft many times, and when I went WOT I noticed how long the fuel kept streaming out. I thought that getting it more fuel for a shorter time period may help out the hole when I just go WOT very quickly.

    I cannot slam open the throttles on my car at low rpm without a brief pause and the taking off quickly. There is definitely a lean spot then it goes back to about 13:1ish.

    This is what I am thinking is happening. I am going wide open on the throttle plates when the volume of air being taken in by the engine is relatively low, so the carb main circuit is not sensing enough flow through the venturi to draw fuel up the main jet and into the etubes and then into the main venturi.

    I am currently running 40 pump jets. I bought 50 pump jets. This will dispense the same amount of fuel but in a shorter amount of time.

    This could have two results...

    I could dump too much and it will not atomize and may pool up in the manifold and make the instant WOT hole much worse. Or it will get the fuel it needs and will fill the void left by going to instant WOT at lower gears.

    It is a calculated risk. I bought 2 sizes up on the pump jet (going with a 50 vs a 45) so I could get a more drastic delta. If it gets much worse I will know I went perhaps the wrong way.

    the beauty of the webers design is to be able to do so much tuning so quickly without removing the carbs. They were made to work on, which gives me a smile each and every time I take them apart. I cannot fathom a more user friendly design.
    1971 240Z HLS30-38691
    93.9% done and getting better every day
    Now with 100% more DATSUN SPIRIT L28 Power
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    Friendly for sure!

    Another way to get more fuel is to buy 0mm bleed-back (pump spill) (pump exhaust) valves for the bottom of the fuel bowl.

    3 X $5

    http://www.piercemanifolds.com/product_p/79701.000.htm
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    Something else you could try to help pouring more fuel would be to close the bypass valve (spill valve) at the bottom of your fuel bowls. You have 1 per carb.

    On mines, previous owner has shut the holes with solder so 100% of the fuel from the accel pump system is going thru the throttle instead of having some getting back into fuel bowl.
    I don't have any flat spot at tip in, except if I try at 2000rpm to hit WOT super fast (something we never do that fast anyhow)
    Last edited by Lazeum; 10-02-2012 at 08:46 AM.
    Matt - 72' 240z

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    Well my my issue I am trying to solve is just what you describe Lazeum, WOT at 2000 rpm super fast. I am not sure I really need to, but something in me just loves to tinker with these darn things! Under normal driving, the car runs almost flawlessly.
    1971 240Z HLS30-38691
    93.9% done and getting better every day
    Now with 100% more DATSUN SPIRIT L28 Power
    1968 Datsun 2000 SRL311-03416

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    Good luck getting racing carbs to act like FI!
    In no way am I being sarcastic , it's just the way I am looking at my triples. Not sure you can get racing carbs tuned well enough to stomp on them at. 2krpm and think they will react the same as stomping on them at 4krpm. At 2krpm there is probably too much fuel for your engine to swallow- thus hesitation. Then your AFRs look way off while the motor is trying to burn off all that fuel.
    Thankfully you enjoy tinkering, because it will take a ton of it!!!
    Steve
    71 240z,bw-5sp 2.4-40 over,balanced,e-88,big valves,ported&polished, stage2,header, triple Mikuni's 40's
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    Unfortunately, I know this is true, but I love it.
    1971 240Z HLS30-38691
    93.9% done and getting better every day
    Now with 100% more DATSUN SPIRIT L28 Power
    1968 Datsun 2000 SRL311-03416

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    Default help!!!!!

    [hello guys i need your advise i have a 2.8 l in my 240z with tripples idle55f8 main 130 air 170 ef16 the car idles perfect when about 1500 stumbles and misses spits up top is fine while cruizing it nmisses now if i pull the choke while it idles the miss goes away but it doesnt idle can somebody help with a diagnosis on what i need to do

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    What size Choke (Main Venturi)?
    What size carb (40,42,45)?
    What model variation if it is a DCOE?

    First step is to set the fuel level to 25mm down from the main jet well on all 3.) Read This: http://www.classiczcars.com/forums/thread47405.html

    Second step is to balance all carbs at idle

    Third step is to ensure all linkages are the same length

    Fourth step is to balance air flow at 3000 rpm with linkage adjustments.
    Last edited by Blue; 10-07-2012 at 02:39 PM.
    There is scarcely anything in the world that some man cannot make a little worse, and sell a little more cheaply.
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    Agreed, the more info you have the better. Also, do you have a wideband?
    1971 240Z HLS30-38691
    93.9% done and getting better every day
    Now with 100% more DATSUN SPIRIT L28 Power
    1968 Datsun 2000 SRL311-03416

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    How do you guys balance carbs at 3000 rpm? If I try with my sk meter, the meter is off the scale and unreadable. Also how do you keep it at steady 3000 without using throttle stop screws and messing up balance at idle or am I missing something? I just visually balanced throttle linkage operation and its pretty good but maybe it can be better. Its perfect at idle as far as balance goes. Milgeo....from a seat of pants tuner, I would try going up on idle jet and see if it makes a difference. Are your plugs on the white side after idling for a few minutes?

    Brian

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    Default dcoe

    goodmorning just waking up for work
    well they are 45s dcoe i dont know the variation have to check venturi is 32 the carbs idle just fine they work fine up top in between they spit and hessitate if i pull the air they are fine no spitting but they wont idle does that mean that can be jetted out by changing the idle jet to richer?

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    Stephan, just back from the first Triple Trouble Carb Clinic. Big news for you, Keith will work with you until you get it right. You can just pay for shipping stuff back to exchange the Hypojets you don't need. Second bit of big news is he will be looking into making Hypojets for Mikunis.

    I can't believe the difference in my carbs! Not much difference in the top end, but wow do I have a crisp and quick responding bottom end and midrange! Highly recommend Hypojets!
    Rob
    2000 BMW R1100 RT-SE (for sale)
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    1973 Datsun 240Z Restoration project. New paint in original white. E31 head on 2.4 block. Nissan Motorsports header. R200 with Nissan motorsports LSD.

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    I was looking into those, but the prices get big quick.
    Rob, can you tell us what you were running prior to the hypojets?
    1971 240Z HLS30-38691
    93.9% done and getting better every day
    Now with 100% more DATSUN SPIRIT L28 Power
    1968 Datsun 2000 SRL311-03416

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    Also, listing which hypojets and hypo etubes will be an initial starting point for:

    Stock 240z 40DCOE 28mm choke
    Stock 240z 40DCOE 30mm choke
    Stock 240z 40DCOE 32mm choke

    Stock 280z 40DCOE 30mm choke
    Stock 280z 40DCOE 32mm choke
    Stock 280z 40DCOE 34mm choke

    Stock 280z 45DCOE 34mm choke
    Stock 280z 45DCOE 36mm choke
    Stock 280z 45DCOE 38mm choke

    3.1 litre Stroker

    Would be nice to see!
    There is scarcely anything in the world that some man cannot make a little worse, and sell a little more cheaply.
    The person who buys on price alone is this man's lawful prey.


    John Ruskin (1819 - 1900)



    ZCars in Eastern Canada seaport ready for shipment to Europe

    http://ZSportCanada.com


  100. #100
    Registered User LeonV's Avatar
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    Apr 2009
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    My setup:

    • L24/E88 with stock cam
    • 40DCOE18 Webers with 30mm chokes
    • Nissan Motorsport header with dual 2" pipes all the way back

    Started with:

    • 50F9 idle jets (too rich)
    • F11 e-tube (junk)
    • 170 air corrector
    • 125 mains (bit rich)

    *** I need to track down accel pump specs

    Performance resulted in really soggy idle and cruise mixture and some bogging on aggressive tip in at lower rpm. WOT above 3500rpm was good, no matter the gear or how aggressive I was with the throttle.


    After tuning day:
    • H223 hypojets (.022" orifice, 3rd air hole)
    • O3 e-tube
    • Custom air corrector for O3 tube
    • 125 mains


    Idle is way better, less soggy but no flat spot. Cruise mixture is better but still rich. I plan on going to a smaller hole on the hypojets, which would enrich the idle but lean out cruise. I think the H222 or H221 setting will get me close but we'll wait and see.

    At WOT, my mixture still tends to go richer as rpms climb. I'll talk to Keith and see what he thinks. I'm thinking this may require a different e-tube, perhaps an O2, as it has less holes to lift the fuel up. However, low and midrange is fantastic. The mixture is spot on with much less jumping around as shown by my wideband.

    I still have an initial hesitation issue when quickly going WOT. It'll hesitate and then pick up, so this points to an accel pump issue. I need to investigate this further, as I don't know how much bleed-back I have and don't remember the size of my pump jet (40 or 45 I think).

    One other thing I discovered a few days ago is that my internal return springs need replacement. I was doing idle-sync and decided to see how well each carb returns. After disconnecting the linkage, I blipped each carb independently to see if it had the same airflow before and after. Each carb was flowing more after I blipped the throttle, indicating that it is not fully returning. Pierce Manifolds has the right ones for a good price.
    2/74 260Z

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