The first place to look would be the carb. Once it starts, have you adjusted the idle circuit? It should need about 3/4-1 full turn richer. I would also try raising your carb. needle to the highest position. The jug kit will need to be re-jetted but these tips may help confirm that. Don't run it lean cause it WILL burn the piston. Try these 2 things, and either open the jet manually, or get a few up sized jets, and it will come together. Also do you have any idea of the clearance between the piston top, and the cyl. head?