Ok I got an 04 yz450f that I cannot get to run right on the bottom. No matter what I try, rich main lean pilot/rich pilot lean main it ALWAYS studders at like 1/8-1/3 throttle opening at a constant position. As soon as I stop opening(AP OFF) it starts to rich studder. I can manage to get passed it if I open the throttle quick enough but I would like to have it dialed. Specs: First set up: Main:175 Pilot:42 Needle position: clip 4 Starter:72 Elevation: 0-1,500' Full white bros pipe With this set up it studders very bad at any constant throttle position. Had to go up this far on the main to get smooth decel and it still has a little backfiring under decel. Spec 2: Main:170 Pilot:48 Clip #4 everything else the same. This time it has a little less studder at 1/8-1/3 constant throttle with no backfiring on decel and the top end is much much better than a 175&172 If I go down to a 45 pilot it runs crisp everywhere but runs excessively hot and has excessive backfiring.. Can't richen air screw enough. With the 48 pilot i cant turn the air screw in enough to kill it. The 45 will die when I turn it in. So my thought is the pilot air jet needs to go up a size then perhaps go up to a 175 main? Who here knows about tuning the pilot air jets?