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Thread: What main Jets?

  1. #1
    Nova Scotia,Canada,Earth Blue's Avatar
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    Default What main Jets?

    presently

    40DCOE151

    125 main
    170 corrector
    F11 emulsion

    30mm Choke

    4,000 RPM 11.5 Air/Fuel
    6,000 RPM 10.5 Air/Fuel

    240z L24 270 cam

    I am thinking that a switch to 115 may lean it towards 12.5 at 4k and at the same time tip the the high end back at 6k. Any suggestions?
    Last edited by Blue; 09-16-2012 at 01:26 PM.
    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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    ZCars in Eastern Canada seaport ready for shipment to Europe

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    Registered User Lazeum's Avatar
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    Rich at high rpm could very be your chokes being undersized also but 11.5:1 at 4000 is too rich, I would go down to 115 since you have a lot a fuel to restrict to get back to proper AFR at WOT.

    here is a graph with my previous setup with F54/N42, Schneider stg 2 cam & 40DCOE-18. You can see the difference in AFR between mains.

    Click image for larger version. 

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    Last edited by Lazeum; 09-16-2012 at 02:14 PM.
    Matt - 72' 240z

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    Supporting Member Zedyone_kenobi's Avatar
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    I tend to agree with Lazum. I think you should try 115 or 120. I have some 120's if you would like to try.
    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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    Thanks Lazeum. That is the data I wanted to see. 140 to 130 raised your AFR by 1 point. I should do the same and try a 115.


    Stephen, I'll accept your offer and PM my contact info.

    I bought 55F9's and 60F9's based on your data. Mine ran rich and richer. But I ran into 3 problems (Murphy's Law) while on the road testing so I'll go again next weekend and post the data. I just put the 175 fuel needles in and the Solex FPR.

    THANKS!
    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


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    Supporting Member Zedyone_kenobi's Avatar
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    Yeah, I figured out that tuning for steady state cruise in 4th gear is not really the best way to get the idle circuit to work. Shooting for 12.5:1 at 55 mph in 4th gear meant I was pig rich the second I wanted to accelerate in 4th gear while still in the idle circuit.

    The thing is I was reading around on some tuning forums in the Subaru community I am part of. During steady state cruise the engine is under next to no load. Running at 14.5 to 15:1 is fine in the mid range rpm bands if the engine is under next to no load. I would not want to be there at top end. But running right at stoich. while not accelerating is probably a GOOD thing.

    I put 50F9 jets back in mine. But now that I have gone to 32mm chokes, I will probably need to go to 55F9's if the choke has any effect on the progression circuit.
    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

  6. #6
    Registered User Lazeum's Avatar
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    For what is worth, with the curves shown above, I was running around 14:1 to 14.5:1 at crusing speeds. I was running 45f9 if I'm not mistaken (or 50f9 if not 45f9)
    Matt - 72' 240z

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    Registered User LeonV's Avatar
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    On a non-catalyzed vehicle, run it as lean as possible without misfire at cruise for optimal fuel mileage and least emissions. There is no good reason to aim for a rich AFR at cruise, or at idle for that matter. WOT is another story, 12.5-13:1 is a good place to be.

    I'd go with the Subaru guys' recommendation if a catalytic converter were involved, which of course is not the case for a 240Z.
    2/74 260Z

  8. #8
    Registered User Lazeum's Avatar
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    Usually on our cars with no programmable ignition (as far as I'm concerned, it won't be true anymore in some months ) or without depression in the dizzy, timing is way to low to provide good burn at low loads. To compensate for the deficiency, AFR needs to be richer than 14.7.

    Catalysis reaction only occurs at 14.7:1 AFR, that's why car with catalytic converter have always an O2 sensor; it is to allow the ECU to run in close loop mode to regular AFR to be as close as possible to 14.7 ratio.
    Running leaner than 14.7 on our car is creating more NOx & CO2 but less HC & CO but to a small step which makes it not so interesting. See the graph below.

    Click image for larger version. 

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    Last edited by Lazeum; 09-17-2012 at 12:13 PM.
    Matt - 72' 240z

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    Registered User LeonV's Avatar
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    Quote Originally Posted by Lazeum View Post
    Usually on our cars with no programmable ignition (as far as I'm concerned, it won't be true anymore in some months ) or without depression in the dizzy, timing is way to low to provide good burn at low loads. To compensate for the deficiency, AFR needs to be richer than 14.7.
    I don't have that problem!



    Quote Originally Posted by Lazeum View Post
    Catalysis reaction only occurs at 14.7:1 AFR, that's why car with catalytic converter have always an O2 sensor; it is to allow the ECU to run in close loop mode to regular AFR to be as close as possible to 14.7 ratio.
    Running leaner than 14.7 on our car is creating more NOx & CO2 but less HC & CO but to a small step which makes it not so interesting. See the graph below.

    Click image for larger version. 

Name:	AFR_Emissions_Graph.jpg 
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    Let's compare 12.5 and 17 AFR on the chart you posted:
    • CO is way lower
    • HC is slightly lower
    • NOx is about even
    • CO2 is about even


    Comparing running 14.5 AFR with 17AFR:
    • CO is slightly lower
    • HC is slightly lower
    • NOx is slightly higher
    • CO2 is slightly lower


    Plus, you get an additional benefit of higher mpg.

    You're right about requiring more spark timing with leaner mixtures and lighter loads, but that is why I recommended to run as lean as possible without misfire (or losing power). Certain combinations will be able to attain leaner mixtures than others, depending on mixture distribution, spark timing, combustion chamber design, etc.
    2/74 260Z

  10. #10
    Registered User Lazeum's Avatar
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    I'm wondering if I haven't heard stuff about extr lean AFR to run modern engine. I think direct injection fuel engine are working also with those kind of AFR. I'll have to look for some info but it would make sense.

    For your Edis system, I know that too well You've shared this picture with me already and I'm going to follow your steps towards EDIS & Megajolt also
    Matt - 72' 240z

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    Registered User LeonV's Avatar
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    Quote Originally Posted by Lazeum View Post
    I'm wondering if I haven't heard stuff about extr lean AFR to run modern engine. I think direct injection fuel engine are working also with those kind of AFR. I'll have to look for some info but it would make sense.
    DI engines can run very lean but the idea has been around for a long time, e.g. Honda's CVCC!

    Quote Originally Posted by Lazeum View Post
    For your Edis system, I know that too well You've shared this picture with me already and I'm going to follow your steps towards EDIS & Megajolt also
    Good choice! MJ is great, just finished a 1000 mile road trip to JCCS and back. My speedo doesn't work for now, hence I don't have a working odometer to track mpg. However, it is definitely improved and I'm somewhere in the 20-30 mpg range . Once I deal with the speedo, I'll have a better idea.

    From memory, I'm running 42deg advance at cruise but my AFR is way too rich (about 11.5:1). I'm attending a DCOE tuning day here in Northern CA (that conedodger has organized) in October. I'll be aiming for far leaner cruise while keeping transition tractable and WOT around 13:1.

    Let me know if you have any questions about EDIS and MJLJ, I'm happy to answer. I've got more details posted in my thread at hybridz.org.
    Last edited by LeonV; 09-17-2012 at 03:00 PM.
    2/74 260Z

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    Registered User Lazeum's Avatar
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    I won't go off topic then on this post. I'll go on HBZ if I've got questions
    Looking forward for the tach to work since this is the little unknow for now (I took the tach adaptor with my kit)
    Matt - 72' 240z

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    Registered User LeonV's Avatar
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    Quote Originally Posted by Lazeum View Post
    I won't go off topic then on this post. I'll go on HBZ if I've got questions
    Looking forward for the tach to work since this is the little unknow for now (I took the tach adaptor with my kit)
    Yeah, the tach is the last thing to figure out. I'll post up when I solve it.

    Well, the thread has been thoroughly derailed! As to the original post, find the main jet which gives you 12.5-13:1 AFR at WOT. The e-tube/air jet combo will control the slope of the AFR curve.
    2/74 260Z

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    Nova Scotia,Canada,Earth Blue's Avatar
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    it was a great derail because I never knew of MegaJolt JR. I was reading about MegaSquirt a few days ago and wondering about using it for spark only.

    Now a fun project for the winter.
    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


  15. #15
    Nova Scotia,Canada,Earth Blue's Avatar
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    Follow up.

    Thanks Stephen, the 120's did the trick. I tried 115's with 170 and 180 air. They just seem to have a little less torque in the 4.0k to 6.5k rpm range. The 120's seem to be the sweet spot. Just trying the different airs to see the effect on high rpms.

    A/F is ~13.5 in the upper rpm's with the 115's and ~12.0 with the 120's.


    btw I am cruising at 12 A/F on the highway and 12 A/F at best lean idle so the 55F11 idle jest's are too rich. I need 50F11 or 45F11's for this one. I can turn the idle mixture in 1/2 a turn to get 14.7 at idle but I still get 12 A/F at cruise.


    After the experimentation to date I think the idle jet should be selected and optimized for cruise then the idle mixture's final set up shold happen AFTER the best idle jet for cruising is found. The idle jet should not be selected at idle as the mixture screw can pay havoc.
    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


  16. #16
    Registered User Lazeum's Avatar
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    Regarding idle jets, I had good luck on several L-engine with f9 units (I'm running 50f9 with fully built L28). I can hit the trottle with no bog easily.
    Engine is ultra smooth to drive since I've got distributorless ignition (running 49 advance at cruise)
    Matt - 72' 240z

  17. #17
    Nova Scotia,Canada,Earth Blue's Avatar
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    I tried 55F9 but too rich.
    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


  18. #18
    Supporting Member Zedyone_kenobi's Avatar
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    49 degrees! Great googly moogly
    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

  19. #19
    Registered User Lazeum's Avatar
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    This is what the engine likes so it is. Why not 50 if you ask me? just because...

    If you want to know more => Autosportlabs - 240z with MJLJ
    Last edited by Lazeum; 08-03-2013 at 10:22 AM.
    Matt - 72' 240z

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