JD, I have a yfz450 that I cant get quite right. I have tried many needle and jet combos but still have a rich condition at one particular spot. At light throttle low load, like 1st gear just off idle I get a rich studder. It is not detectable when riding hard, just when returning to the truck. I am beginning to think it might be the the exhaust. Have you had any problems with pipes causing flow disruptions at certain rpms?