Some will remember that I had problems with plug fouling and odd running behavior with my '01 426. A CDI swap (free from Yamaha) seems to have mostly cured the problem. During the 'discovery' period Yamaha had me try different pilot jets and also a different accelerator pump diaphram. Initially I didn't notice much change from the diaphram but as the weather warmed up the bike developed a very rough off-idle condition. I changed the pilot jet from a 45 back to the stock 42 but no amount of tinkering with the pilot screw could get rid of the problem. In fact, if I gave the throttle just a small blip it was possible to stall the motor. However, when I replaced the 'trial' diaphram with the original the problem mostly went away. The motor still feels a bit rich - 'burbley'- off idle but it still runs pretty well. Now just yesterday I was talking with one of the folks at the local Yamaha dealership and he mentioned that another new '01 426 had developed a bad plug fouling problem. Yamaha is going to swap the carb because the bike idles even when the pilot screw is turned all the way in. Ah ha! So naturally I went home and tried the same trick on mine and it too idles with zero turns on the pilot screw. This indicates an internal fuel leak in the carb. The leak in my carb is probably smaller as the bike works best when the pilot is 1 1/2 turns out but the problem will probably get worse as the weather warms up. Has anyone else noticed this on their bikes? If you get a chance try turning the pilot all the way in and see if your bike still idles. I'd like to correlate the condition with those who can't seem to get a tan colored plug (always a little sooty).