mad is correct. the only way to get real increases in power from this motor is to change the cam, increase the displacement (big bore), carb, ignition, and then exhaust. from there you'd have to get exotic (read expensive) to increase the power. remember it's all about getting as much air/fuel into the motor and then igniting it and moving it out. the more you get in (displacement, carb, cam) the bigger the bang (ignition) and then the more have to get out (exhaust). the least expensive real power difference is the BBR 120cc big bore kit:
http://www.crfsonly.com/catalog/product ... ts_id/1226
this is a great kit because it comes with the big bore cylinder, high compression piston kit, high performance cam, high performance valve springs, rockers, and gaskets. here's a product review do did for this kit:
http://crfsonly.com/reviews/bbr/big-bor ... review.php
this kit would be a good place to start.
ken