This is such a great site! You guys are doing an awesome service, however, I guess it is fortunate for me (so far) that I did not stumble on this prior to buying my new 01 426 (15 Dec) or I may have kept my old YZ250! I have about 1 hour time on the bike (due to the unusually heavy winter weather we have experienced in this part of Texas the last 2 weeks) however, and performance wise it has defineitly met my high expectations! Of course, I am running into the same sooty/fouled spark plug scenario most of you mention, but man does this thing pull hard! BTW, I am at about 3000 ft elevation, and so far averaging 45-50f temps. I have the airscrew 2 1/2 turns out (with great response), raised the clip one position and dropped the main one size. My feeling from reading most of the posts in this forum (heck, I have read them all!) is that this seems more of an ignition problem that carb, but who am I to say! My only other changes so far were swapping the stock bars for McGrath bend Renthals, getting rid of those atrocious tires (all of the tracks I ride are soft/intermediate terrain which are usually prepared well) for Michelin S-12's (that front tire has helped every bike I have ever used it on). I also plan to go to a different clamp to move the bars up (best improvement I ever made to my trusty 94 YZ). I also followed the advice I read about greasing all bearings (the steering stem and wheel bearings were DRY!). So far very happy! There are several great tracks/riding areas in the Texas/Northern New Mexico area if anyone ever gets out here, happy to advise anyone.