Amen to everything that Team Bolt has written.
A couple of things to note:
The reason that powervalves are fitted is to vary exhaust port height. The power curve of a two-stroke is basically governed by the exhaust port height ( amongst other things of course), but exhaust port height is a *major* consideration.
Low port height is *great* for low speed work, and a high port height is *great* for high-speed stuff, and its also very closely tied in to the tuned length of your exhaust pipes....so using a powervalve gives you the best of both worlds........as pointed out above, ensuring that the powervalves are fully clean and carbon-free is a *huge* consideration, they must be able to freely move throughout their full range, in order to work properly.
My favourite book on the subject is " Performance Tuning in Theory & Practice", by A. Graham Bell - ISBN 0 85429 329 9
This book is invaluable if you really want to get your head into 2-strokes and tuning, performance mods etc etc. There are full chapters on porting specs, expansion chambers (exhaust pipes), carburettors etc etc.
One word of warning - don't be sucked into believing that 'Bigger is Better' when it comes to carbies or porting.......this is not always the case, and in fact is often not the case at all......
Happy tuning mate, there is *hours* of endless fun

if you really want to give it all a nudge......
