I don't know about what the pros of this site are going to say, maybe they will say add the crank and do some port and polish and milling but I think thats the most expensive. Some cheap ways are the basics air filter , exhaust pipes , jets , reeds , coils ,cdi box , spark plug ( no one is going to believe me on that one but I'm putting an e3 plug in mine because everything else I have that plug in it works great..even my snow blower what a difference) and an adjustable stator , higher octane gas like 93 , I think thats everything before you touch the engine.You can change the front sprocket to 14 if you done most of whats on that list..at least thats what I did. ...To bad I don't know how to list all of these things ,like everyone else does when they add their posts...