Some other folks have said this before and I would like to reiterate this fact: It is very easy to jet too rich. Both my buddy on a YZ426 and my WR felt jetted correctly, and we both couldn't start the bikes due to plug fouling after about 60 mile over on several rides. We both made changes, not too radical, and ended up rich with the fouled plug as the witness. I think the 50 pilot jet idea on the '00 is terrible advice, even the 48 ran very rich over time. I even fouled it with a 45/172/4th clip sotck needle and the pilot screw way out 2 3/4 (Wr time, airbox lid off, exh. baffle removed;600 feet 70 dgrees, low humid). Guys if you are running a 50 check your plug! Someone mentioned recently that the bike should start on choke, rev up a bite and run crappy for the first few miles then run better as the engine fully heats up. I definately agree with this, my overall jetting seems better when this happens, and all my other bikes behave the same way. I think I am going to start draining my carb after riding-less chance of having fuel slosh while trailering. Just to note: my jetting specs are now: 45PJ, 170MJ, 1 7/8 Pilot screw, 4th clip stock '00 needle. It runs good, will do a plug check before I have to this at the track again! ('oo wr timed, restictions removed, 600feet, 70 degreees, low humid), but I think this is close.