I would check your needel settings on both top an bottem end. Look at your carb. Make sure that the Air Filter is cleen, make sure there is nothing in the carb, an that it opens an closes smothly. Also make srue your Idel is set coretly.
2 full turns and like te other guy said check every screw on the motor even the head bolts i bought a brand new motor and the head bolts were loose and the carb bolt that held it to the motor was loose.