dnmac, the condition you are describing is called pre-det. or predetonation. it happens to the big bore high compression 2 strokes when you don't use fuel that has a high enough octane rating. the lower octane fuel ignites at alot less compression which is known as spontaneous compression combustion. basically the fuel is detonated before the piston is in the right location on the up stroke which puts major downforce on it as it is still on it's way up putting tremendous stress on the piston, head, gaskets, bearings etc... when you lean up the mixture in the carb. ,it will get even worse. if the pre det. or pinging is allowed to continue, you will probably be rebuilding your engine soon wether you want to or not. these bikes are built to perform and the big performance costs big money. pay for some quality high octane race fuel in your bike and the problem will surely go away. or you can run lower octane and you'll end up paying big money anyways to repair the damage done to your engine. trust me i've seen it. hope the info helps, MADDOGGY
