lonerider65 wrote on 07/20/11 at 13:14:18: Turning the air fuel screw doesnt seem to have any effect. Its so rich that it will foul the plug after a while, but it doesnt backfire. What gives?
backfire (technically, to be correct, afterfire) is caused by being overly lean.
what happens is the engine misses, the gas vapors collect in the exhaust, when enough oxygen is drawn in, a spark from a non miss lights it and bang.
so being incredably rich, there's no miss fire, no oxygen, no bang... no joy.