I have and 03 450 that I bought new. Ive never modded it much until recently when I got back into dirt riding. It has the airbox snorkel removed and holes drilled, a white brothers air filter and e series exhaust with all the discs in, and gray wire cut. Currently it has a 152 main, 48 pilot, 65 starter, 70 paj, 70 leak, and was 3.5 turns on the pilot screw. I have never felt any off idle stumble but just constant throttle stumble. When riding at constant throttle, 1/4 throttle, it stumbles but if I pull the choke it runs better, even when warmed up.