454 backfire

[DavidB]

Buddy has a 454, unknown internals, long headers, 3" exhaust, true duals, no cats, no x pipe, mini flowmasters with turndowns, no tailpipe. Runs good except it backfires only out the driver side when you romp on it and let the throttle snap shut. If you close it slower, it doesn't do it, and it doesn't do it with the air cleaner off. They checked the valves and I fixed an exhaust leak and it still does it. Running rich, but only one side is doing it.

Ideas?

Thanks

 

[juggalo_wa]

did it just start doing it? you might just notice it more with the flowmasters on it than you would normally. maybe not enough backpressure?

 

[Greg72]

Keep the throttle mashed.....don't ever lift.

 

[sweetk30]

if lots of miles and orignal cam. i bet the exaust lobes are going . bbc eat cams faster than sbc . pull the valve covers and roll motor over by hand and watch all the rockers for same basic lift. if some are less cam is shot.

 

[Tominator II]

I have an old 454 that backfired when coasting down hills at highway speed. I tried different ways to make it stop for a long time. It was funny if Lance Armstrong wannabes were on the road when I coasted by downhill. I finally tried new sparkplugs instead of cleaning and regapping the old ones, that fixed it. No more backfires.