I just found this site yesterday and am impressed by the by all of the kind people who have replied to questions. I have a 98 YZ400 and am going to pick up my 01 YZ426 this morning. I have never fouled a plug on my 400. I am a bit concerned after I read all of the posts regarding fouled plugs on the 01 426. 1. What causes the fouling? 2. What is he solution? I do know that the air filter (when freshly oiled) can cause some difficult starting. I cannot believe that the 426 would be that much different than my 400.