K&N filters work pretty good, most of the time. some bikes just don't have enough clearance between the frame and carb. I ran a K&N on the '99 tomos I had. removing the factory P.O.S. air box and putting a K&N was worth 5mph by itself. if you plan on any SERIOUS mods, consider a aftermarket filter.
Whatever you do, DO NOT RUN THE BIKE WITHOUT AN AIR FILTER. It takes a TEASPOON of dirt to totally RUIN an engine.