My 2001 YZ426. Stock except for an FMF Ti4 pipe. Not sure on the jetting. The bike starts easy, has great power but....when riding at a steady RPM, say down a dirt road or whatever, it misses. It only does this when holding a steady RPM. I've only had this bike for about 2 months and I'm new to Yamaha's so I don't even know where to begin. My buddy also bought a used 01 YZ426 at about the same time I did and his does the same thing. Any suggestions?