I've tried other jetting settings tonight in order to get rid of the bog. Seems to be a rich bog since 1) it becomes worse as the engine gets hot 2) rising the needle worsen it. 01WR426 yz timed, air lid removed, FMFpc4, stock header, 0-1000', 40-85 deg. So far I've tried 170mj with combinations of clip 3 to 5 and PJ 45 and 48. I know that the bike pulls very hard at 170mj, clip 4, 48 pj but the bog kills the engine as soon as the throttle is wacked.My latest attemps were worthless. The timing of the pump is finely tuned now and the squirt is thrown right under the slide as soon as it clears up. Next step, will do the BK mod. Can somebody tell me why the BK is effective? I mean why does reducing a squirt from 4 sec to 1 sec would get rid of a bog that occurs within a millisecond after the throtle is wacked. The bog is already happening way before 1 sec. I really don't get it. I rather think the flow is too big. I wish I had a leak jet on this 426. Can somebody explain why 426s don't have those leak jets. I'm even thinking about checking the valves back again.