i've got a 99 kdx220 and it does something similar, pings or knocks at wot, my bike has airbox mod, rb carb, boysen reeds, fmf rev pipe, weisco piston, and i just took my top end apart and cleaned the kips, still does it... it's like it's doens't really have much of a top end, which i guess might be the case cause of the porting of the 220, i'm thinking of sending my clyinder and head to frp to have them done up, hey what are you running for jets?, i'm at i believe about sea level and i'm running a 40 pilot and 150 main with the airscrew about a turn and a half out