You are much better off to buy an assortment of main jets online or from the dealer. They are anywhere from $3 to $8 each depending on source and several will cost less than a "jet kit". You need to learn how to do a propper plug chop to verify your jetting, recommendations will get you close...but, the exact jetting your bike needs will depend on many variables. And as Samolia said, a main jet merely corrects your air-fuel ratio for your existing mods to prevent engine damage or fouling of plugs.