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

[Smirnoff]

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!

[angrystroker]

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

[cffisher]

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

[Smirnoff]

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

[34_40]

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

Maybe. It may only act up while running.

[Smirnoff]

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!!!!!

[robtcjm]

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.

[34_40]

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