99 rm 250

It has a powervalve. I don't know which way to adjust it. The reeds open on every revolution of the crank, about the only tuning you can do on them is to install different reeds. Stiffer one's generally resist flutter and make more top end power, while softer ones are more responsive at low rpm. The Boysen power reeds are made of two parts to try to get the best of both worlds and seem to work fairly well.

good luck

You can change the opening of the power valves by adjusting the tension of the spring attached to the main power valve shaft which goes crossways across the top front of the motor and is held in position by two small bolts through a plate. loosen the bolts and turn the cover with the tab on it, I think its clockwise to increase spring tension ( later opening ) and vice versa (to increase spring tension go in the direction of the arrow). Be careful when re-tightening the screws, Suzuki seems to have used some sort of ally colored cheese during manufacture and thet easily strip the threads.

I worked with a friends 98 model with the same powervalve. We liked his at 3/4 out from fully turned in. The difference was not giant no matter what we did.