Here is a thread that will help you with your gearing problem.
save the clutch
Then the next thing you could do is to get rid of your stock exhaust for a stock cag exhaust. The exhaust on thse things are awful. Then theres lightening your clutch and flywheel, better reeds, porting your stock carb and many others. These quads have the same engine as cags so go to the air cooled section and search, start in the how-to section. There is a ton of things that can be done to get you going. I have swapped gearing to 6-78, lightened my clutch and flywheel, ported my carb, did the polini reed mod, ported my e-port, took off one ring, squish at .52 and running a slightly modded cag exhaust an I must say I am very pleased with how my quad is running. If there is anything that your interested in doing try and search for it, but if you can't find it let me know and I can explain things more thoroughly for you.