in my 77 f250 i just put in a 75 ish 460 with fresh bearings and rings to replace my blown up performance 460. its running good but it has an issue with backfiring out the exhaust on deceleration and going down hill especially when i gear down. I lowered the idel from 800 to 650 and that helped but its still very noticeable, the engine is all stock except for a performer intake. the exhaust is l@l fender exit headers with 2.5 inch pipe going through (i think there called pro flo mufflers) there pretty quiet there 22 inches long by 14 wide.


what can cause this?



-gbm-

 

Timing chain ?

 

Could be an exhaust leak, typically at the headers collector gasket, sucking in fresh air during deceleration and mixing with unburnt fuel causing a backfire or "popping".

 

Possibly idle mixture adjustment, base timing or valve timing.