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Thread: Calling all triple carb experts

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    Registered User NismoZ's Avatar
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    Default Calling all triple carb experts

    Ok I recently bought a set of Dellorto 40 carbs for my 240z.. Then engine is a stock L28E long block with headers and exhaust. I need to know what should be the correct jetting for these, Im trying to find out what the ballpark figures should be before i bolt them up and have drivabilty issues..

    I know its not really possible to say what exact sizes should be used do to sea level, location and the weather but i think any experienced tuner could give ball park figures to work with.

    With all that said the carbs are Tuned with 32 chokes, 57 idle jets, 132 main jet, 180 air correction jet, 38 pump jet and #11 emulsion tube and 5 progression holes.. How does this setup sound?


    I am Located in the Sunny So Cal in LA

    Thanks

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    There's a great thread on HybridZ on triple carb setups, I'm sure what you are looking for will be in there somewhere: http://forums.hybridz.org/showthread.php?t=93343

    But FWIW, your setup does sound in the right ballpark.

    Mine are Weber 40s (so I'm not sure how comparable they are to Dells) but mine are 32mm choke, 50 idle jets, 125 main, 175 corrector, #11 'tube. Checked out on the dyno just fine. Motor is a mild L28. If the Dells are the same, then I'd say you're starting point would be close to the money.

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    If you don't already have it, grab a copy of HPBooks "How to Modify Your Nissan/Datsun OHC Engine" -- very helpful book. The below formulas are gleaned from there. A narrow band oxygen sensor in the exhaust can help you tune idle and cruise jetting, a wide band can help with power settings. Dyno time is extremely helpful, albeit expensive.

    40mm carbs are small for best high RPM performance on an L28, but are streetable. 44 or 45mm carbs would be better.
    • Main Venturi size should be around 36mm.
    • An initial main jet choice would be .04 times the main venturi size (or 1.45 in this example)
    • An initial main air correction jet should be .2 larger than the main jet (1.65 in this example).

    Search the forums for jetting recommendations for Mikuni, Weber, Solex, or Dell'Orto (they all work off of the same principles).

    For reference, my jetting is:
    2.4L w/ triple 44mm Mikuni's, header, headwork, etc.
    • 34mm Main Venturi
    • 1.50mm main jet (note that the initial recommendation formula gives 1.36)
    • 1.80mm air correction jet (still tuning this - I may need to go a little larger to maintain high RPM mixture).
    • .65mm pilot jet
    • .45mm pump jet
    • 1.6mm starter jet (rarely use the "choke" system, so not that important)
    • Idle air ports enlarged from 1.2mm to 1.3mm to give better mixture under light cruise acceleration.

    Some examples of jetting I've noted from other posts:
    A Nissan Tech with an L28 was using:
    • 37mm Venturi
    • 160 Main
    • 180 Air
    • 55 Pilot

    Mikuni default jetting for the 44mm carbs (seem set up for an L24):
    • 34 Venturi
    • 150 Main
    • 200 Air
    • 57.5 Pilot
    • 40 Pump

    Nissan Motorsports 16010-E4620 carbs came set up for an L28;
    • 37 Venturi
    • 175 Main
    • 250 Air
    • 55 Pilot

    I believe Jon Mortensen noted he was once running an L28 with:
    • 37 Venturi
    • 155 Main
    • 210 Air
    • 67.5 or 65 Pilot
    • 50 or 45 Pump

    Good luck to you
    Thanks,

    Bob

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    Registered User NismoZ's Avatar
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    Thanks Guys... really appreciate the help. I do happen to have the "How to Modify Your Nissan/Datsun OHC Engine" book and I just orderd the How to power tune Weber & Dellorto carbs... Im glad to hear i should be in the ball park.

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    Quote Originally Posted by NismoZ View Post
    Thanks Guys... really appreciate the help. I do happen to have the "How to Modify Your Nissan/Datsun OHC Engine" book and I just orderd the How to power tune Weber & Dellorto carbs... Im glad to hear i should be in the ball park.
    I did the same thing as you...worked out the jetting based on the books and Weber rules of thumb. And when I put the car on the dyno to check the tune, the guy said "don't change a thing...it's fine the way it is" Old school rules of thumb appear to still work in a digital age

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    I've learned how to tune my carbs with a wideband (Innovate LM2).
    Kind of expensive but I've learned a lot in the process and I had a good time doing it + I know some basics about tuning now
    On the other hand a good wideband is not more expensive than a dyno session with a tuner.
    I found the process to be very rewarding when I was doing a good change (90% of the time). Car screams and feels strong!

    FYI, I had a L28 high comp / mild cam (I had since combo was not so great because of low timing to fight knock):
    40's Weber with 32mm venturi, 45f9 idle jets, 135 main, 180 air, F11 emulsion tube & 45 Accel. Air jets should be a step higher (195)
    Last edited by Lazeum; 01-20-2010 at 01:06 PM.

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    Any of you guys know if the fuel banjos from weber fit the dellortos?

    Im looking for banjos Like this

    http://cgi.ebay.com/Dellorto-DHLA-Ca...item439bc19e82

    My carbs are currantly equipped with three banjos like this

    http://cgi.ebay.com/Dellorto-DHLA-Ca...item439bd48235

    Hopefully i could find some here in the states that are not overpriced
    Last edited by NismoZ; 01-21-2010 at 07:21 PM.

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    Quote Originally Posted by NismoZ View Post
    Any of you guys know if the fuel banjos from weber fit the dellortos?

    Im looking for banjos Like this

    http://cgi.ebay.com/Dellorto-DHLA-Ca...item439bc19e82

    My carbs are currantly equipped with three banjos like this

    http://cgi.ebay.com/Dellorto-DHLA-Ca...item439bd48235

    Hopefully i could find some here in the states that are not overpriced
    Ill Take that as a no i guess... anyways im still waiting on the book i ordered so i will need to ask some questions on the floats..

    How do you set them on the Dellortos? I was told 15mm gap between lid gasket and top of float 23mm float drop.. sound right to you?

    And if they need to be adjusted how do i go about doing so? I know im suppose to bend it somewhere but where..and how?

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    Quote Originally Posted by NismoZ View Post
    Ill Take that as a no i guess... anyways im still waiting on the book i ordered so i will need to ask some questions on the floats..

    How do you set them on the Dellortos? I was told 15mm gap between lid gasket and top of float 23mm float drop.. sound right to you?

    And if they need to be adjusted how do i go about doing so? I know im suppose to bend it somewhere but where..and how?
    There are 3 float weights available, 7.0 grams, 8.5 & 10.0. These weights should be marked on the bottom of the float.
    Distance settings should be carried out by holding the carb cover vertically with the gasket installed so that the measurement between the gasket and the float should be:- 10gram, 16.5-17.0mm, 8.5gram, 15.5-16.00 and 7gram, 14.5-15.00mm. Tweak the metal "ears" to achieve this. The "ear" should be just resting against the needle valve during this operation.

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    Quote Originally Posted by Nigel1943 View Post
    There are 3 float weights available, 7.0 grams, 8.5 & 10.0. These weights should be marked on the bottom of the float.
    Distance settings should be carried out by holding the carb cover vertically with the gasket installed so that the measurement between the gasket and the float should be:- 10gram, 16.5-17.0mm, 8.5gram, 15.5-16.00 and 7gram, 14.5-15.00mm. Tweak the metal "ears" to achieve this. The "ear" should be just resting against the needle valve during this operation.
    Thanks Nigel, now what about the float drop? does it really matter?

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    Quote Originally Posted by NismoZ View Post
    Thanks Nigel, now what about the float drop? does it really matter?
    25mm.

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    Quote Originally Posted by Nigel1943 View Post
    There are 3 float weights available, 7.0 grams, 8.5 & 10.0. These weights should be marked on the bottom of the float.
    Distance settings should be carried out by holding the carb cover vertically with the gasket installed so that the measurement between the gasket and the float should be:- 10gram, 16.5-17.0mm, 8.5gram, 15.5-16.00 and 7gram, 14.5-15.00mm. Tweak the metal "ears" to achieve this. The "ear" should be just resting against the needle valve during this operation.
    Thanks for the help Nigel, Just to clairifiy what exactly do you mean by The "ear" should be just resting against the needle valve during this operation? Does that mean right as it touches the round head but no compressing the spring??
    Last edited by NismoZ; 02-08-2010 at 04:05 PM.

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    Quote Originally Posted by NismoZ View Post
    Thanks for the help Nigel, Just to clairifiy what exactly do you mean by The "ear" should be just resting against the needle valve during this operation? Does that mean right as it touches the round head but no compressing the spring??
    Correct!

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    OK, i got everything installed started it up and what do i hear? my Z that sounds like a Subaru and a SQUEAK SQUEAK to go along with it . I got a vacuum leak at the intake manifold... how reliable is the surface on a TWM intake manifold? do they need to be surfaced prior to installation. any suggestions?
    Last edited by NismoZ; 02-23-2010 at 11:38 PM.

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    Are you sure it is a leak? Use a hose with one tip close to you ear and the other one where you beleive you might have a leak to make sure about it.

    Other solution is to spray some carb cleaner and check how engine react (if it revs, you have a leak)

    You should also have some gasket there. You might want to try to tighten up a little the studs. If it is between carbs and manifold, try to turn bolt by half a turn (do not compress them completely if you don't want to crush the o-rings you most likely have in between)

    How is your timing though?

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    Quote Originally Posted by NismoZ View Post
    OK, i got everything installed started it up and what do i hear? my Z that sounds like a Subaru and a SQUEAK SQUEAK to go along with it . I got a vacuum leak at the intake manifold... how reliable is the surface on a TWM intake manifold? do they need to be surfaced prior to installation. any suggestions?
    A friend of mine had a leak like that on 44 Mikunis, sounded like a mouse or a bird was under the hood. Turned out to be a leaky throttle shaft. He didn't care because his was a race car and it's WOT most of the time.

    If you're sure it's at the manifold, put a thin layer of silicone on each side of the insulators and that should prevent it. You could lay a straight edge on the manifold and see if it's warped, but the TWM stuff is usually pretty good from what I've seen.
    Jon

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    Quote Originally Posted by jmortensen View Post
    A friend of mine had a leak like that on 44 Mikunis, sounded like a mouse or a bird was under the hood. Turned out to be a leaky throttle shaft. He didn't care because his was a race car and it's WOT most of the time.

    If you're sure it's at the manifold, put a thin layer of silicone on each side of the insulators and that should prevent it. You could lay a straight edge on the manifold and see if it's warped, but the TWM stuff is usually pretty good from what I've seen.
    Crap I hope its not the throttle shaft... all the carbs have been rebuilt so they should be good.. what I did notice was as the car was running i could see it was a little wet in between # 1 and 2 on the intake gasket. do most people use silicon seal along with the gasket or is just the gasket usually enough?

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    Gasket is usually enough. I used silicone on the exhaust ports to seal a header. It would probably work on the intake side as well.
    Jon

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    Quote Originally Posted by jmortensen View Post
    Gasket is usually enough. I used silicone on the exhaust ports to seal a header. It would probably work on the intake side as well.
    is there any particular kind i should use?

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    I would use ultra grey on the intake ports, copper on the exhaust ports if you need it. What I did with the copper was to put a really thin layer around the port and then hang the gasket up for an hour or two to dry and then bolt it up. Verify that your leak is really there first though with the carb cleaner.
    Jon

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    Quote Originally Posted by jmortensen View Post
    I would use ultra grey on the intake ports, copper on the exhaust ports if you need it. What I did with the copper was to put a really thin layer around the port and then hang the gasket up for an hour or two to dry and then bolt it up. Verify that your leak is really there first though with the carb cleaner.
    Well I already pulled the carbs off, I couldn't really get it to idle long enough to spray carb cleaner since they are not even tuned yet.. I did notice that it has wet spots on the gasket around the intake ports on #1 and 2 ... is that a good indicator of where the problem lies? i also ran a straight edge across the manifold and they seem to very a little but not much maybe a hair.

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    Quote Originally Posted by NismoZ View Post
    Well I already pulled the carbs off, I couldn't really get it to idle long enough to spray carb cleaner since they are not even tuned yet.. I did notice that it has wet spots on the gasket around the intake ports on #1 and 2 ... is that a good indicator of where the problem lies? i also ran a straight edge across the manifold and they seem to very a little but not much maybe a hair.
    I wouldn't be able to make a good assessment as to whether the wet spots indicate a leak. If it's a brand new TWM manifold I think a leak where the manifold bolts to the head is relatively unlikely, but if you stick a straight edge across the whole manifold you can look to see if there is a gap between the middle runners. If that's what you did and they varied just a hair, I doubt the problem is at the head.

    Using a graphite gasket, or a paper gasket? I had nothing but bad luck with the paper manifold gaskets.
    Jon

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    Quote Originally Posted by jmortensen View Post
    I wouldn't be able to make a good assessment as to whether the wet spots indicate a leak. If it's a brand new TWM manifold I think a leak where the manifold bolts to the head is relatively unlikely, but if you stick a straight edge across the whole manifold you can look to see if there is a gap between the middle runners. If that's what you did and they varied just a hair, I doubt the problem is at the head.

    Using a graphite gasket, or a paper gasket? I had nothing but bad luck with the paper manifold gaskets.
    Its the MSA header Gasket, Im going to take a closer look at it. Since I have the n47 head the MSA gasket only had holes for the fuel injection manifold not the carb. So maybe when I made the the new holes it caused the gasket to not be flat like it is suppose to be.. its the only thing i can think of. Everything from the manifold back is new or rebuilt including spacers.

    Maybe I should have tried reusing the previous MSA header gasket.
    Last edited by NismoZ; 02-24-2010 at 02:28 PM.

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    If it's the white paper MSA header gasket that I had, it sucks. Get a graphite gasket, it's compressible and will seal better and won't crack and cause an exhaust leak like mine did a couple thousand miles after I installed it. That's my opinion anyway, others may differ.
    Jon

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    Quote Originally Posted by Lazeum View Post
    Are you sure it is a leak? Use a hose with one tip close to you ear and the other one where you beleive you might have a leak to make sure about it.

    Other solution is to spray some carb cleaner and check how engine react (if it revs, you have a leak)

    You should also have some gasket there. You might want to try to tighten up a little the studs. If it is between carbs and manifold, try to turn bolt by half a turn (do not compress them completely if you don't want to crush the o-rings you most likely have in between)

    How is your timing though?
    Timing is good. car ran great prior to installing the triples... I got the thackery washers tightened to or around .035 gap so im assuming that the o rings are sealed correctly.

    I have tried to keep the car running but its hard since it just wants to die,when it is forced to run it sounds like its running on 5 cylinders while its chirping, I did try the carb cleaner but could not really notice a difference..

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    well i did the hose to the ear trick and it is indeed leaking at the gasket..there was no other noticeable sounds from anywhere else..

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    Ok I was wrong when I checked the manifold with a straight edge last night, its not off by a hair its more like 50 thou... I rechecked it with 3 other straight edges or levels with the same results and I think it is a little worse than I thought. Since I have never dealt with aftermarket manifolds I snapped some photos for you guys to look at. Is this manifold useless? Is resurfacing it even a option?

    Also the carbs being bolted to the manifold shouldn't cause this right?

    Btw sorry for the large pics but its the only way to see what Im talking about.











    Last edited by NismoZ; 02-24-2010 at 06:06 PM.

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    There's plenty of "meat" there, so I'd try a competent machine shop to get everything laser straight before tossing the manifold for a new one.
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    Quote Originally Posted by d240zx2 View Post
    There's plenty of "meat" there, so I'd try a competent machine shop to get everything laser straight before tossing the manifold for a new one.
    Think so? Im worried it wont be able to be sealed up with the exhaust washers after resurfacing... the flanges are already a little thinner than the original SU intake manifold.
    Last edited by NismoZ; 02-24-2010 at 08:29 PM.

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    Is it new? Can you exchange it for one that isn't warped?
    Jon

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    Quote Originally Posted by jmortensen View Post
    Is it new? Can you exchange it for one that isn't warped?
    Yea it is suppose to be new,and appears to be new. I bought the whole triple setup from a fellow Z member who said it has never been used. So is this manifold junk?
    Last edited by NismoZ; 02-24-2010 at 09:30 PM.

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    There are no balance tubes so I think the bolts will easily pull it flat against the head. Give it a try but tighten it from the outside in. Torque the first and last bolts then work towards the middle. See if that works. Do a dry run with no gasket and check with a feeler after its torqued. If not, have it milled and have the shop make you up some custom stepped washers.
    Last edited by cygnusx1; 02-24-2010 at 09:37 PM.
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    Not junk.
    Jon

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    Quote Originally Posted by cygnusx1 View Post
    There are no balance tubes so I think the bolts will easily pull it flat against the head. Give it a try. I think it will be fine.
    I wish it were so but I have already tried that, it wont seal not matter what I do. I Even tried gasket seal on top of the gasket with no luck It still has vacuum leaks at #1,2,5 and 6.

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    Quote Originally Posted by jmortensen View Post
    Not junk.
    Im Glad to hear that, So what can I do Jon?

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    Quote Originally Posted by cygnusx1 View Post
    If not, have it milled and have the shop make you up some custom stepped washers.
    I edited my post with your option.
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    Thanks for your help guys, I really appreciate it.
    Last edited by NismoZ; 02-25-2010 at 12:49 AM.

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    Well I ended up Belt sanding it with good results. Its nice and straight now. Now all I need is some washers with .125 of an inch step to be able to snug it down. I was thinking on using filed washers but I have to remove half the thickness of the washer to get a step of that size. Would using a washer that thin be a no no? its about .155

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    Wanted to ask a question, is it possible for the fuel level to be to low? I check the level of the fuel in the bowls and the fuel sits at about 30mm -32mm down from the top off the jet tower, Is this ok, to low, not enough? I got the floats set at 15.5mm
    Last edited by NismoZ; 03-01-2010 at 04:37 PM.

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    Quote Originally Posted by NismoZ View Post
    Wanted to ask a question, is it possible for the fuel level to be to low? I check the level of the fuel in the bowls and the fuel sits at about 30mm -32mm down from the top jet tower, Is this ok, to low, not enough? I got the floats set at 15.5mm
    Should be 27mm from the edge of the carb body. Not sure how that relates to the "top jet tower".

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    Quote Originally Posted by Nigel1943 View Post
    Should be 27mm from the edge of the carb body. Not sure how that relates to the "top jet tower".
    Ok so it has to be at 27mm from the side of the carb body, no more no less. I think the jet tower might be a little higher than the sides so ill use the carb body for reference.

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    Thought I would update this, got the car up and running and its driving pretty good. the tuning is in question though as I have lean pops when cruzing or part throttle in one carb, so i pulled the plugs to see what they looked like and 1-4 turned out to be just about right. 5 & 6 is another story, #5 was rich and #6 was lean?, All the linkages are dead on and opening at the same time so im not sure if its jetting or what. Other than that cars runs pretty hard.
    Last edited by NismoZ; 03-26-2010 at 11:36 PM.

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    Maybe float levels are out in the 3rd carb?

    I had that prob too, one carb was leaner than the rest, and in the end the float level in that carb was 3mm out. Once it was fixed the plug colours evened out.

    I'm sure the process of checking Dell floats would be similar to Webers: http://www.webcon.co.uk/Downloads/DC...%20setting.pdf
    Last edited by Babalouie; 03-27-2010 at 06:49 AM.

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    Quote Originally Posted by Babalouie View Post
    Maybe float levels are out in the 3rd carb?

    I had that prob too, one carb was leaner than the rest, and in the end the float level in that carb was 3mm out. Once it was fixed the plug colours evened out.

    I'm sure the process of checking Dell floats would be similar to Webers: http://www.webcon.co.uk/Downloads/DC...%20setting.pdf
    ok I will check the level on that carb, btw could float level cause one cylinder to be rich and the other lean? Just thought it was odd since it was like that on just one carb.

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    If it's only one plug that looks lean, I'd be more tempted to suspect an air leak in the manifold. Give your manifold to head bolts a quick visual check? One of my friends had this same issue and when he looked, one of the nuts was finger tight

    ...and at the carb to manifold join, what are you using? Are they are those big o-ring type gaskets?

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    Quote Originally Posted by Babalouie View Post
    If it's only one plug that looks lean, I'd be more tempted to suspect an air leak in the manifold. Give your manifold to head bolts a quick visual check? One of my friends had this same issue and when he looked, one of the nuts was finger tight

    ...and at the carb to manifold join, what are you using? Are they are those big o-ring type gaskets?
    Found out the problem was the air bypass valve was open leaning it out at idle..

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    Ok so I'm extremely frustrated, I took my car to a Z specialist, He was recommended to me for tuning my triples, $250 later Im still having issues, it coughs misses and backfires at low end. the only time it runs ok is half to full throttle. I was told this is normal for triples to do sometimes? After taking it to the place to get tuned Im still in the same situation I started... no new jets, still runs ruff and is pissing me off.

    I even started to mess with it myself and actually got it to run better, But I only have a syncrometer so I can only adjust flow... I don't suppose there is anybody near the 90638 area that could give me a hand is there?

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    Are there ANY Weber techs or guys who know their way around 40DCOE's in Washington State? I'm not rich but could do some trade work, buy ya lunch, something.

    It's hard to get her to idle below 1100 and there's a flat spot on light throttle. It also lags at heavy throttle. Installing an electric fuel pump today to try and feed it better at higher RPM's but think the issue is elsewhere.

    Where should my timing be?
    Stock L24, 142,000 miles on her with stack of service records, E12-80 ignition, stock cam, 3-into-2 header with 2.5" exhaust.

    170 Air Gap
    120 Main

    choke? 150 and 85 F9?

    Anyone?
    Call me if you'd like.
    360-631-0757 Cell

    Thanks in advance. Heading to the garage.
    Dave
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    HLH info at CZCC Do a search for info on the other upgrades I offer.

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    per phone conversation 135-140 mains 200 air's f-11 tubes. Throttle blades dead center of last progression hole. Idle mixture screws 1/2-1 turn out. If more than that start to look at bigger idle jet. Get those chokes out verify size 30's are small not much top end. 33 good top end low end suffers below 3 grand at more than 1.4 throttle. Get stacks gotta gotta have them.

    I have a set of 200 correctors i will trade for those 170's

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    Timing should be around 34-36 all in run 91+ octane. No vacuum advance. If connected to a log vacuum source its not a strong enough signal. It will scatter timing all over at cruise.

    Here is my setup if i can tune this in for 400+ hp you can do a N/A l24

    http://www.youtube.com/watch?v=YbxYUz77G2Q

    Here is the complete list of idle jet air bleed holes in order from rich to lean

    F6 (richest), F12, F9, F8, F11, F13, F2, F4, F5, F7, F1, F3 (leanest)

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    per phone conversation 135-140 mains 200 air's f-11 tubes. Throttle blades dead center of last progression hole. Idle mixture screws 1/2-1 turn out. If more than that start to look at bigger idle jet. Get those chokes out verify size 30's are small not much top end. 33 good top end low end suffers below 3 grand at more than 1.4 throttle. Get stacks gotta gotta have them.

    I have a set of 200 correctors i will trade for those 170's I actually have a set of 140's i see. 15 bucks for those. Call me if yah wanna send them out.
    Last edited by yetterben; 05-07-2010 at 12:50 PM.

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    Quote Originally Posted by yetterben View Post
    per phone conversation 135-140 mains 200 air's f-11 tubes. Throttle blades dead center of last progression hole. Idle mixture screws 1/2-1 turn out. If more than that start to look at bigger idle jet. Get those chokes out verify size 30's are small not much top end. 33 good top end low end suffers below 3 grand at more than 1.4 throttle. Get stacks gotta gotta have them.

    I have a set of 200 correctors i will trade for those 170's

    I have 170 correctors. I'll trade you for your 200s!

    PMEd you.

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    240Z Elec. Upgrade guy Zs-ondabrain's Avatar
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    Too late, they're on their way to me as we speak.

    Hey Ben, I'll let ya know how it turns out.
    Dave
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