I HAVE BEEN HAVING SAME SPARKPLUG FOWLING, ALSO AFTER ABOUT AN HOUR OF RIDING, I FOUND THE CHOKE CABLE AND THE CABLE HOUSING WAS BROKEN, ALLOWING SLEEVE TO SLIDE DOWN WITH CABLE, AND LETTING CHOKE HANDLE ON CARB TO NOT OPEN CHOKE ALL THE WAY AND LETS CHOKE HANDLE BOUNCE UP AND DOWN ALSO. EASY QUICK FIX WAS TO PUT A SPRING ON CARB CHOKE HANDLE TO KEEP IT DOWN WHEN CABLE IS NOT PULLED. HOPE THIS MAY HELP YOU.