So I completed top/bottom end rebuild. Broke in the new top end at home with all new fluids andspark plug. Went to Blue Diamond MX park today for 1st ride, man was it hot and humid. Thebike started on 3rd kick rode for 20 minutes all was good. Ditto for round two but the thirdtime out the engine was acting up. It was backfiring on acceleration and decel, it wouldbog when you hit the throttle then suddenly rev, in higher gears it would sometimes have nothrottle response. I am at a lost I didn't touch the fuel system during rebuild and beforerebuild there was no problems. It sounds like EFI or old gas but then why was it OK for twothirds of day. Any suggestions?