check your oil/fuel mixture is correct,if so you may need to adjust your high speed mixure screw ,it is one of two screws on the carby marked (H)adjust this screw while the throttle is in fully open position.wind screw out slowly until motor starts to splutter then wind in slowly until motor runs on song.stop winding in as soon as motor is on song or motor will run to lean and over heating will occur.
todd
December 2007