If you know that your fuel lines and tank are good i would put a new plug in get the motor UP TO TEMP(190-200) set the high speed then go to your low speed after clearing motor out STOP and do a 10 sec count u want a clean crisp take off you can also do the pinch test ( let the motor idle down and pinch fuel line bout an inch from carb it it should rev just a bit and die it should do this around 4-5 sec this works for me. change ur exhaust gaskets too hope this helps you