Can anyone explain what the small adjustment **** on the left of the cylinder does? I know it's for the powervalve but have always been told to not touch it. Nobody ever seems to know why, they just tell me to stay away from it. If it's an adjustment, what and how does it adjust? Can the powervalve be "fine tuned" to fit your riding style, etc.?

 

That **** sets the preload on the powervalve spring. It's best to leave it alone unless the engine, exhaust, and fuel system have been highly modified......

 

The **** adjust spring tension on the exhaust valve, which in turn controls at which rpm it opens and how fast. If you have stock pipe, leave it alone-at the 250 mark. Stock setting is one turn counter clockwise until it lines up to that mark. If you have a pipe and carb or porting done it needs to be adjusted. to adjust, you need only to loosen the 2 screws then turn COUNTERCLOCKWISE. Mine is piped, ported and carbed. I turned mine about 3/4 of a turn more. Now it opens up more in the miderange for a better kick. It is more of an experiment to just keep adjusting until you like it. It only take 60 seconds to adjust.
At Idle, my exhaust valve opens at 4950 rpm's(I have a Tiny Tach on my Quad)