I also posted this in the jetting forum. A friend has an 02 WR426. He removed the airbox and was running the stock pipe with baffle removed. It ran fine. It took a spill and trashed the pipe. A good reason to replace it with an FMF powercore 4. We assumed we would need to increase the jet size. It came stock with a 165. We tried a 175 and a 170; both made it cut out at mid to high rpm. It seemed to run best (although still cut out) with the stock 165 main jet. Do we need to go smaller?