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Thread: Backfiring while driving, not while sitting still?

  1. #1

    Backfiring while driving, not while sitting still?

    Hope someone here can help me out. I built a 351w, and after finally getting everything put together, it ran great for the break-in. Sitting still, it runs and sounds great. Problem I'm having is when I'm driving it's backfiring out the carb, but only while accelerating. Timing is set right, all vacuum lines are new, new fuel tank, lines, filter, complete new motor, trans, carb, etc. I'm bangin' my head on the wall now trying to figure out why it won't do it while sitting still in my shop, but as soon as I get on the road, Pop.


    Anyone have any ideas to help a youngster out?

    Thanks!

    John T.

  2. #2
    Senior Member MASTER BUILDER
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    timing advance module bad?
    oil pressure constant? keeping a intake v open at high rev?

  3. #3
    Senior Member RACING JUNKIE
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    Check your firing order sounds like spark plug wires crossed. If that doesn't fix it pull the valve covers and look for broken parts.
    good luck

  4. #4
    Senior Member MASTER BUILDER
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    ....Am i right this only happens under load in drive.....might want to ck the adjusters on the intake valves....either too tight or broken and not holding setting

  5. #5
    Well...not the adjusters, checked them earlier in the evening. Also put a different distributer in it just to make sure it wasn't the pick-up coil. Rechecked the firing order, and all the plugs/wires. No broken parts under the valve covers - everything looks great and new.

    Hmmm...bangin my head against the wall one more time. It did start doing it in my shop while in park, but only while revving the motor.
    Any other ideas would be greatly appreciated.

    Thanks again!

    John T.

  6. #6
    Senior Member RACING JUNKIE lively's Avatar
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    IF IT IS UNDER LOAD THE ONLY THING HAS TO BE SOME SORT OF ELECTRICAL MALFUNCTION :shock: :shock:

    I HAVE SEEN A WEAK BATTERY CAUSE THIS SAME THING TO HAPPEN IN A GRANPRIX I WORKED ON :evil: :evil:
    JUST A THOUGHT BUT MIGHT BE WORTH CHECKING!!

    LIVELY

  7. #7
    Senior Member RACING JUNKIE
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    Quote Originally Posted by lively
    IF IT IS UNDER LOAD THE ONLY THING HAS TO BE SOME SORT OF ELECTRICAL MALFUNCTION :shock: :shock:

    I HAVE SEEN A WEAK BATTERY CAUSE THIS SAME THING TO HAPPEN IN A GRANPRIX I WORKED ON :evil: :evil:
    JUST A THOUGHT BUT MIGHT BE WORTH CHECKING!!

    LIVELY
    Lively is on the right track I think, low voltage could cause a problem.


    I had one setup that ran fine sitting there but when you got into it, it'd miss ended up being plugs. Assuming you have checked them all, and ohm'd all the plug wires ? What ign setup are you using ?
    David Lanning
    IHRA NHRA 387B

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

  8. #8
    Administrator RACING JUNKIE bjuice's Avatar
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    flat tappet or roller camshaft ?

    flat tappets were bad about knocking lobes off camshaft resulting in the backfire your speaking of.

    Next i would check Timing chain, also did you degree camshaft ?

    i would rule out electrical 1st..but would look here in the end if the rest doesn't clear it up

    food for thought.
    Bjuice..

    "I'M YOUR HUCKLEBERRY ! "

  9. #9
    Senior Member RACING JUNKIE lively's Avatar
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    ANOTHER THING :shock: :shock: --IS IT A MISS OR A DEAD STUMBLE?? ARE YOU RUNNING A CAM OUT OF A 351W OR FOR A 302? DIFFERENT FIRING ORDERS!!!

    LIVELY

  10. #10
    Senior Member RACING JUNKIE
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    i had that problem one time with the spit fire spark plugs,
    went and bought the reliable a/c and that fixed my problem,
    sounded like the timing was off, bad spark plug, might
    check that, i zapped my hand checking plugs, man what
    a charge


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