hey guys, just a quick summary of what happens with the 98 and earlier yamaha power valves, the stop on the left side of the bike is behind the powervalve cover, it is the black circle with the screws on either side, if you pull that off you will see on the inside there are two metal tabs that stop the powervalve from rotating. after a while the constant pounding on the tabs creates and indent and that can cause the powervalve to hit the piston, the stops on mine were worn down about an 1/8th of an inch and the piston had signs of contact with the valve. So I'm going to replace the powervalve and the stop plate itself, I urge anyone with these bikes to check this out immediately. post if you have any questions on how to do this, it was pretty simple and I'll get back to you on pricing.
Jeff