cc - i am familiar with a 2 stoke that is 4 stroking - most commonly (not only though) from a rich mixture which can cause occasional incomplete combustion...let me step all the way back. I rode the bike for about 200 miles with no problems. On the last day of my trip, the trail back home took us through some deep stream crossings....On one crossing as I brough the bike back up to speed, the engine's RPMs soared - like the slide in the carb was stuck wide open...so I killed the bike, started it back up and the ride continued. When I returned home, the bike had very little power in the high RPMs - most of my riding is tight trails so I could short shift the bike all day long and never notice the problem until the fire roads home when I would wind it out - when you would expect the powerband to come alive, it wouldn't. So I pulled the top end, mic'd the piston and confirmed it was in specs. I expected the obvious - excessive carbon on the p-valve and to not even be able to manually move it. I could - it moved freely. So I pulled it apart, scraped what carbon was on it clean - inspected everything, reassembled and threw in fresh rings. After reassembly, a fresh plug and another carb inspection, the problem was still evident - which is why I am starting to think it migth be ignition related...in the meantime while waiting to get a hold of another bike to start testing parts on, I thought I would throw this post out there...see if anybody had any kind of igniter problems or the like. And my real question - does anyone know how to test these units? If I'm not mistaken the bike uses a magneto supported CDI igntion - could it be possible the electronic advance is not occuring properly. I'm sure some will say I'm reading way too far into this but I think of myself as a fairly competent mechanic - I've done numerous top end and complete rebuilds and this one has got me puzzled. I am pretty sure I have checked the obvious but please feel free to point anything out that I may be missing.