This is actually pretty embarresing, I am a motorcycle technician and ended up purchasing this bike that blew a hole through the center of the piston. I have done the following: carburetor overhaul & dipped in carburetor DIP, replaced timing chain, new piston & rings, new valves, cut new seat to make sure they sealed properly. I am getting spark, fuel and compression. The cam chain is perfectly alligned. I go to start it and it wil fire for 1 revolution of the engine, then backfire. Anyone ever experence this problem and find out what was wrong? Any feed back will be greatly appreciated.