anything from #54-#56 depending on your altitude and plug chop results. there is no set number jet that you need to use. its a trial and error sort of situation. you have to install a new jet, then install a new spark plug, run the bike full throttle for at least one mile, then remove the spark plug and see what color it is. you do this with each different size jet and a new plug until you get a nice even tan color on the plugs ceramic core. white or grey= too lean. black and sooty= too rich. improper jetting will cause a siezure.