I just rebuilt my 1989 Yamaha blaster. Ran fine idleign and when I went to go ride it after the heat cycles it sputtered and the accelerated and did that on and on. Then it fouls a spark plug after the engine heats up but not before it sputters and blows air out the back pipe like it is back fireing. Is it the carb over filling the engine making it foul the plugs and back fire?