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Thread: stumble from start to 200 feet

  1. #1

    stumble from start to 200 feet

    My question is about a hesitation / stumble from the starting line to 200 feet on the track.
    I have a 582 BBC, 15.1 compression, 12 degree profiler heads, HRE sheet metal intake, 2 -1150 holley carbs ( 9377 ). I had a single 1250 carb on this engine and the car ran fine--7.27 at 184 mph. I switched to the 2-1150 ( apd ) carbs and I have developed a stumble from the starting line to 200 foot on the track. I have tried 2 fuel systems. 1- a belt drive fuel pump with a bypass regulator. 2- a barry grant 400 pump with quick fuel regulators ( one to each carb). so I dont think the issue is with the fuel delivery.
    I have tried raising the fuel level from 3.75 off the top of the bowl to 1,2 and 3 flats richer. the issue is still there.( now the issue is a rich condition after the burn out. The carb is back to one flat richer, fuel just trickling out of the site screw. my jets are 92 square in both carbs, the idle air bleed is .052, intermediate is .043 and the high speed is .029. I have a 2 speed power glide with a trans brake, the coverter stalls at 6700 rpm. I have not changed anything else on the combination, just the carbs. If you have any thoughts on this issue I thank you. Rick

  2. #2
    Senior Member DYNO OPERATOR
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    First of all 7.27 ET at 184? were you pulling a trailer to get the MPH so low for that ET? I have to believe that your engine hates the new intake configuration and likely has a reversion wave or the carbs are not even close to having the correct fuel curve for your engine set up. Did it run great on the dyno? If you have not tuned these carbs and intake on the dyno, that would be my next stop to save your entry fees and wasted time at the track. That single carb set up is awful impressive in a DOOR CAR at 7.27ET.
    Are there any electrical draws on the battery at the same time this problem occures? Sometimes the battery will dip in voltage and create a ign misfire condition during the run. Are the wedge shaped floats in the correct side of the carb? In East and West carb applications we use wedge shapped floats to prevent the bowl from running dry on acceleration.
    Bruce

  3. #3
    the car is a rear engine dragster @2100 lbs, not a door car.
    the floats are in with the angle to the rear. the battrey drain I dont think is an issue. I have not had the engine on a dyno. I have thought about putting it on the dyno, and probably should.

  4. #4
    Senior Member DYNO OPERATOR
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    Quote Originally Posted by verklerracing
    the car is a rear engine dragster @2100 lbs, not a door car.
    the floats are in with the angle to the rear. the battrey drain I dont think is an issue. I have not had the engine on a dyno. I have thought about putting it on the dyno, and probably should.
    When you said angle to the rear did you mean the narrowest part of the float is pointing to the rear. If so that is correct. Otherwise good luck on the stumble. Sometimes these things can be caused by one simple item and other times by ten marginal adjustments working against each other. I hope you find it soon. The ET makes more sense in a dragster, Thanks for the clarification.
    Bruce

  5. #5
    Senior Member RACING JUNKIE
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    Your leaving on the trans brake so idle screw adjustment or squirters won't come into play. What about a fuel sloshing problem, I'm thinking either sloshing fuel from the jets closest to the front of the car or sloshing fuel out of the vent tubes in the venturies.

  6. #6
    it could be a fuel sloshing issue although I have run the fuel level at 1 flat to 3 flats rich and it makes no difference. we run 1.10 60'. I know guys running harder 60' then that with a simalar set up and have no issue.

  7. #7
    Senior Member RACING JUNKIE
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    Your up to 6700 rpm when you leave, the converter is not going to let the rpm get any lower than 6700, the car runs fine down track, so you electronics are right I think its a G force issue. I've seen a rubber hose across the vent tubes work before. You need jet extensions with a 90.lol. And I don't see alot of 7.20 racecars.

  8. #8
    Senior Member DYNO OPERATOR
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    Just a thought, If you have larger than #6 lines ( #8 ) supplying the bowls like you did with your single carb, that required them. The larger line will cause a significant fuel pressure spike if a front mounted fuel system is used. This condition is necessary to keep a single carb supplied with fuel at the bowl during launch. With dual carbs the fuel consumption is 1/2 per carb now and the fuel spike at launch could be giving a dose of fuel it can not use now or control. I would run near 6.2 PSI with dual carbs and #6 supply line and NO FUEL LOG. These things can cause problems that the other set up needed to run correctly. Go back to the 2 flats above level or set them on the bench with a 3/8" drill bit or piece of bar stock like you used to. The lower fuel pressure is easeier to control and can easily keep up. You will know if it is lean due to the lower fuel pressure because it will drive to the 100' where you are unable to get to now, but it will be fine. 6.2 is high pressure for dual carbs with .375 float settings.
    More things to ponder.
    Bruce

  9. #9
    Bruce

    I have the fuel psi to the regulators at 20 psi and at 7.5 to 8 psi to the carbs. I do run #6 line. #10 to the fuel pump, #8 to the regulators and #6 to the carbs. I will try the 6.2 psi and the float setting. thanks for the thought. Rick

  10. #10
    Senior Member RACING JUNKIE
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    Rick you have a pm
    David Lanning
    IHRA NHRA 387B

    Fleenor Racing Transmission
    419-280-1406
    Lanning Electric
    Complete Drag Car Wiring
    APD Race Engines
    www.apdracing.com


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