Car leaning out under load/sudden throttle
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  1. #1
    1000+ Posts Dave's Avatar
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    Default Car leaning out under load/sudden throttle

    Hi Guys,
    I finally finished installing my A/f meter and took the car for a drive.
    When cruising the a/f ratio is good, and when taking off in 1st gear with full throttle through 1st and 2nd gear the mixture is correct.
    However, i am having problems when accelerating from a rolling start; when i stab the throttle the mixture leans right off immediately and doesn't really recover which causes the engine to ping. I can push very lightly on the accelerator and get it to accelerate without leaning off, but as soon as i give it a little more throttle it leans off badly.
    I have checked the accelerator pump and its squirting a good amount of fuel.
    Does anyone know if this is a normal trend in carburettored cars?
    If not any help in rectifying the problem would be much appreciated.

    Dave

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  2. #2
    1000+ Posts alan moore's Avatar
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    In 1st and 2nd, perhaps the A/F meter does not react fast enough, and also the engine is more heavily loaded in the higher gears, that is the motor cannot spin up as freely. I would suggest to go up a jet size or two on the secondary and knock the timing back 2-3 degrees for a trial. Just check too, that the needle valve is 2.25 mm, as you may well be draining the float bowl as you hold your foot flat for longer periods in the taller gears.
    Last edited by alan moore; 5th April 2004 at 11:55 PM.
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  3. #3
    1000+ Posts Dave's Avatar
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    Alan,

    The guage has a digital readout which refreshes slow enough so it can be read by the human eye, however it also has a bar of led's that move very quickly so you can see the trend of what the mixture is doing almost instantly.
    I dont think the problem is to do with the fuel bowl draining as i can drive at high revs for a long period at high speed without the mixture going strange.
    Looking at the bar of led's, when I press the throttle down it instantly leans right off and slowy climbs back to rich again.
    Is this a normal trend for a carburettor or is something set up wrong or blocked??

    Thanks again,

    Dave


  4. #4
    Fellow Frogger! GavinS's Avatar
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    Sounds like a pain, has it ever work as it should? meaning the jets are sized ok.
    Have you considered checking the distributor in combination with the carby, does it rev freely with the clutch in? faulty vacc advance switch can do weird things.
    Have fun with it and stay
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  5. #5
    Budding Architect ???? pugrambo's Avatar
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    is the secondary opening up properly ?

    it might be a bit slow and hence leaning out till it gets going maybe
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  6. #6
    1000+ Posts PeterT's Avatar
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    Quote Originally Posted by pugrambo
    is the secondary opening up properly ?

    it might be a bit slow and hence leaning out till it gets going maybe
    Remember the engine now has different fuel requirements (cam + compression) than it did as standard. Sounds like you're going to have to start playing with jets and tubes. If the mixtures are OK at cruise, then the primary main jet is OK. I'd be looking at the transistion from idle to the mains. You might be able to fudge it a bit with more idle mixture, but only so far.

    By "stabbing" do you mean squeazing it in gently, or dumping it?

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  7. #7
    1000+ Posts Dave's Avatar
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    This is happening on the main throat, i'm not opening the secondary at the moment.
    If i just lean on the throttle ever so slightly i can get it to stay rich. but if i put the accelerator down more than 1-2cm quickly it quickly leans off.
    At the momend the main jet in the primary is 112 and the 2ndary is 120. So far trying to solve the problem i have richened up the float level and tried a 120 main jet in the primary aswell.
    All this did was make the engine run richer under all circumstances, however it didn't solve the problem because as soon as i used any throttle it leaned right off as bad as before

    Thanks for the help guys,

    Dave


  8. #8
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    Dave, what about going up one or two sizes on the pump jet?

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