Backfiring 350

[skyshark186]

This is actually kinda pissing me off. It didnt backfire till I had it tuned to pass emitions, now i cant get it to stop. I readjusted the carb so it is running better and backfiring less. It still gives a resounding pop if it hit the gas hard then let off quickly. Its got an HEI system on it and the plugs are carboned to hell, maybe the HEI needs replaced? Really doesnt use oil, but smokes because of the incomplete detonation. Thoughts?

 

[kc_chevota]

sounds like a streched timing chain. also check the timing

 

[skyshark186]

no timing light. Got a buddy though. Ill have him come by this week. Thanks, well check the chain while were at it. Didnt even think of that.

 

[Gumby]

Backfire through the carb, or through the exhaust? Carboned up plugs kind of keeps it away from a lean backfire. Sounds like you might be getting unburnt fuel in the exhaust that is lighting off. An exhaust leak providing oxygen in the exhaust can cause that to happen.

 

[skyshark186]

Yeah....it fires out my left pipe. Left pipe only. I need to reweld the hangers on that side. They are getting pretty weak. Maybe ill check the manifold bolts. Thanks again

 

[skyshark186]

We have a winner. Gumby hits it on the head. Manifold bolts finger tight on both sides. Enough air leaking in i had to readjust my carb after i got it sealed again.

Add to the list, loose motor mounts, retightened the oil pan bolts(new gaskets a week ago), loose starter bolts, loose power steering pump bolts, and a loose lower tranny plug and youve got one very badly maintained 350. Looks like the PO drove this thing for 5 years without ANY maintenance whatsoever. Tightened every bolt, nut, or screw i could find. Thanks guys.