Beware when buying spare plugs, as the dealer may sell you too cold a heat range--which will lead to plug fouling. The dealer parts manaul lists a CR9E for the '01 426. However, my bike was delivered with a CR8E and the service/owners manual also lists a CR8E as the correct plug. If you run a "9" heat range plug, it will definately foul faster than the proper "8" series. In fact, woods riders and others that aren't riding at continous WFO, can probably get by running a CR7E. This is because--like all manufacturers-- Yamaha is going to play it safe and install a plug cold enough to prevent preignition even when ridden in the deepest, fastest sandwash possible. Slow speed riders don't need that huge safety margin.