the best mod for this bike is a torque converter, enough torque to pull up the front wheel and enough speed to keep up on a city road, they run around 130 $ for a china system and youll never regret buying one. i can also suggest a number 90 main jet, exhaust and an aftermarket airfilter. better yet, heres how to do the linkage for no governor
http://diygokarts.com/vb/showthread.php?t=15203 and please tighten up that chain, its way to loose, you should only have 1/2 slack. if you plan to do alot of wheelies, you may want to reinforce your mount. after the TAV and even before i cracked the front left corner of mine doing them. also take out the throttle stop screw when is right by the throttle arm, and no matter what is said. unless you plan on going with a billet rod and flywheel dont change your valve springs. valve float occurs at 5500-6000 rpm and will save the flywheel and rod from going, if you change them the valves wont float and you will have a chance of blowing it if you dont have proper upgrade parts