Try cleaning the air breather its a small black box on the back of the carb(only use petrol).If this dosent try cleaning out the carb as there may be dirt clogging up the fuel flow from the jet.To Clean Out the carb empty the mini motos petrol turn it upsidedown and unscrew the two screws at the bottom of the carb(leave the middle one in place)place the parts you take out on a clean cloth and be sure not to lose them. When the bottom piece is removed there should be a gold coulered jet and a float inside give this whole area a clean with petrol and put back pieces the exact way you found them.
Chris
July 2007