The more hrs I put on my '02 426 the worse it seems to run. I keep thinking the jetting's to blame cause it seems to run lean but that's never been changed since I got it dialed in originally. My valves are in spec and the overall condition of the bike is good. When I go out for a full day of riding it's always strong in the morning but as the bike gets hot on the afternoon rides it starts to miss and sputter like it's lean. I adjust the fuel screw but it doesn't help. I'm wondering now if it's piston related and I'm asking how to tell if it needs replacing. The manual says replace as needed and believe it or not (in an '02), I'm still running the original piston. Should I get a leak-down test done or could this be something else?