400 engine and clutch mod opinions

[jethrow]

I need help with directions to rebuild a 2000 Xplorer 400. It is bone stock, with alot of miles. This bike is 4x4, hi/lo and lbs @ 588. Runs great, but needs tuning. I would like it to stand straight up when I punch it in low, instead of slowly hitting in. High range seems fast, but with no good downshift. I would really like to learn how and where to build this bike to keep up with: 750 Brute Force, 800 Sportsman, and King Quad. I wouldn't mind out running them either. Thanks for your help if you reply.