I just installed a new wiseco piston kit im my '98 200, cleaned the powervalves,(all 3 of them) but the main valves were so heavily coated with carbon that I had to chip some off before I could remove them, apparantly the previous owner had never cleaned them. But it was nothing a scratch awl, carb cleaner and a stiff wirerbrush over 1/2 hr couldn't cure. I checked for up and down play in the connecting rod, there was none, so I can rule out piston slap I used 2 cans of carb cleaner and a good 1/2 gallon of kerosene to make sure all parts of the jug were spotless. used 2-stroke oil to lube everything as I put it back together. She fired up on the 2nd kick (gotta push some fuel throught the carb ya' know), and runs stronger than when I first got her. gobs of bottom end, pleanty of powerband, and still the rattle.