Hey guys I've got my engine rebuilt an back in and it's running. There's a backfire at idle only, it misses a little but gets way better after you hit 3,000 rpm, and the backfire at idle is inconsistent. When I first start it up it won't do it for a few seconds 30- 1 minute, them it backfires it sounds like when it cones to a certain cylinder. I think it's an injector staying Completly open but I'm not sure. I know its running rich (100 miles and almost on empty) any help would be apprieciated

 

is the motor stock? check the heat on each cylinder on the exhaust, are any of the exhaust manifold pipes getting red hot?