what they said. check for vac leaks also.

my 440 backfires out the driver side only.

but mine is an exhast leak at the rear of the driver exhast manifold.

bang all 3 gears at WOT and let all the way off with a snap,then wait a few seconds and bang like a shotgun. then maybe a couple more if I engine break it all the way down form the WOT blast.

I did a drive by of my buddys with it in 2nd and reved up, killed the key pump the throttle,hit the key and made everyone on the carport dive for cover.

sounds like a SHOTGUN BLAST every time.I have blown muffs apart fliping the key to pop it,but the glass packs are holding up for now.

could be the 3x18 echo tips that make the bang loud.