Thanks for the advice on where to start.
Mods on his quad: Full Toomey T-5 pipe kit, Uni Air Filter(s), MotionPro Twist Throttle and idle kit, I believe that is the pertinent info. We bought his quad used and we were told it was set up for racing--all I know is he goes fast and leaves me behind easily. We will be purchasing the compression tester tomorrow and will work on it Monday & Tuesday (clean and repair days) and we will go from there. Once again--Thanks!!!