Backfiring while driving, not while sitting still?

Old 11-16-2008, 04:03 PM
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Trailerpro
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Default 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.
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Old 11-16-2008, 09:48 PM
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poncholvr
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timing advance module bad?
oil pressure constant? keeping a intake v open at high rev?
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Old 11-17-2008, 12:24 AM
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dparker
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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
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Old 11-17-2008, 05:01 PM
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radicalz
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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
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Old 11-17-2008, 06:25 PM
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Trailerpro
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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.
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Old 11-17-2008, 06:43 PM
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lively
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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
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Old 11-17-2008, 06:46 PM
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hammertime
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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 ?
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Old 11-17-2008, 06:50 PM
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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.
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Old 11-17-2008, 06:54 PM
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lively
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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
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Old 11-17-2008, 06:59 PM
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signsbyesa
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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
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