Just picked up this 2003 Polaris Predator 90 for my soon to be eight year old son. He is loving it. Its a big step up from his Suzuki LT 50. Hope to do some riding at some sand pits sunday, videos to follow.
first and easiest upgrade for quick power increase is remove rev limiter, there is a wire clip you remove off the cdi box. then get a uni filter to fit right onto the carb which I believe will be a 16mm carb, likely mikuni. I think the id of the filter will be 1.5" then put a 105main jet in it and a 22-24 pilot. I am in Florida so jetting may be diff where you are. But that will get you some nice gains. When you are ready to see it pull the front end up let me know, i will steer you right.