Ports - Your port heights determine your power band for the most part. The higher the port, the higher the power band. If you take the head off your motor, and push the piston down to BDC with your finger, you'll notice the transfer ports and part of the exhaust port is still covered. If you have any, use a spare cylinder base gasket to raise it a bit. This will give you a higher power band AND allow your motor to breathe better, provided your piston isn't blocking your intake. Your exhaust and transfer timing will get longer (pushing your power band up), but unless you have reed valves, your intake timing will get shorter (lowering your power). Get some reeds, and reed port, and try this instead of dremeling your cylinder.
Pipe - This can override your porting job, if you have one, make sure its tuned to the same RPM as your pipe for maximum power. You have no idea what RPM a pipe is tuned for with these motors because the specs arent listed. Building your own costs significantly less (about $25 if you can find sheet metal and pipe) and you can tune it exactly how you want (broad power band, but low boost, or a short power band but lots of boost [most of the pipes you find will be this second one])
Carb & intake manifold - To go that fast you'll need to be able to breathe easily. A larger carb and larger intake will allow the motor to suck all the air it needs. 21mm piston port should net you close to or beyond 11k RPM, but will require a larger intake manifold to match. A 21mm carb should be matched with a 21mm I.D. (25mm O.D.) manifold. A 1" copper pipe should meet these specs. Avoid sharp bends, 7 degrees at most unless its a smooth curve, any bigger angles and you'll cause eddies to form and cause drag in your intake (which is part of why these motors have trouble breathing, the stock intake has an angle of 30-40 degrees, way way waaayyy too much).
Balance - Cannot stress this enough: These motors can shake themselves apart at 8000 RPM, if you're aiming for 11k, you'll want to balance. I've done this through piston weight reduction, however you can also drill your crank, as theres only so much of the piston you can remove before you comprimise its strength, or start to need reed valves. I do have reeds, and after I get my titanium wrist pin, and perhaps a bushing (because the reeds allow lots of lubrication, which bushings need), my piston should weigh around 86 grams, a whopping 24 grams less than an unmodified piston. This combined with a jag CDI, my bike runs smooooooth. Problem is the jag CDI isn't designed to go to 11k RPM, it'll retard way, way too much. So you'll need a new CDI as well (the stock one will destroy your bearings in no time at those speeds too so dont even try that).
