Thread: Need Help - Exhaust Backfire & Pop-ing.....

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Have a 1970's vintage crate motor (350/290HP) with headers & an Edelbrock 600 CFM carb (1406).

Motor had no issues until I started it after sitting in the garage for 1-year, runs rough & "backfires" through 1 side of the header exhaust (passenger).

Steps so far:

1. Drained all of the gas & refilled with premium, runs a little better, but still idles hard with a small miss & exhaust backfires loud upon deceleration (passenger side only). Sometimes while running at idle, it will also pop a little on the passenger side only.....

2. I tightened all of the header bolts, none of them were loose, & looked where a possible leak could be. Everything "looked" normal?

3. I pulled the plugs - they all are black. So I bought a new set, gapped them, but have not installed yet.

Am I on the right track to find the root cause of the exhaust backfire? What else should I check or eliminate as the root cause?

I was recently laid-off from work & want to get the vehicle running like a clock before Spring is upon us.....thanks in advance!

Cap arcing, needs to be driven, sticky ex valve?

Check for vac. leaks. as said before sticky valve??

Will a compression test validate or eliminate a sticky exhaust valve?

Originally Posted by Smirnoff

Will a compression test validate or eliminate a sticky exhaust valve?

Maybe. It may only act up while running.

Update:

Today I changed the old plugs (AC Delco R45TS) with a new set of NGK UR4's (Gap .045), another member suggested the NGK V's are a much better plug?

Well, the exhaust pop-ing & rough idle appear to be eliminated......at least during idle & revving in Neutral. Appears a fowled plug or plug(s) on the passenger side was the root-cause. I didn't have a chance to actually drive the vehicle because of insurance/car being garage stored during the winter.

Since the plugs were black & fowled - my next step is adjusting the Edelbrock carb to a leaner condition.

Thanks to all who responded!!!!!

Had tthe same thing happen to me. I pulled plug wires untill it stopped popping changed that plug and it stopped. Alot of thing start happening when you dont run them.

That's good news! Thanks for the reply also! Means alot to hear of a resolution.