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w-lewis 03-08-2018 10:44 AM

Backfiring on deceleration
When letting off the gas, decelerating, my 351W backfires through left exhaust only. More of a popping sound and not really annoying, but just concerned I might be damaging something in the engine. Any suggestions as to how to stop it?

patrickt 03-08-2018 10:47 AM

That's almost always an air leak around the collecter/primary pipes/etc. use the Acousti-Seal that is giving fits in this current thread:

w-lewis 03-08-2018 10:56 AM

Thanks Patrick

MOTORHEAD 03-08-2018 11:21 AM

Ck for exhaust gasket leak or intake leak also. l

w-lewis 03-08-2018 11:32 AM

I've tightened all of the accessible exhaust manifold bolts, but unfortunately, most are very difficult to get to, even from the underside when on a lift. At this time, the issue is not bad enough to start removing manifold to check for intake leaks. At this point, I think I'll try the header to side pipe joint first.

Texasdoc 03-08-2018 12:01 PM

Sometimes it is a lean condition. Easy to check and it is reversible. Try richening up the idle mixture just a touch. If it is a standard Holley style carb, turn all (2 or 4) idle screws counter clockwise by 1/8 of a turn. If that doesn't fix the popping on decel, put them back where they were and work on the pipes.

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