Just rebuilt my top end in my 98 yz 250 put a 15t sprocket up front and bike doesn't seem to have much hit in the mid/high dept. The bike sounds extremely crisp and bottom end is pretty strong but when I get on it the bike sounds muffled not allowing any over rev at all, wondering if the power valve could be the culprit? This is the first time I have rebuilt this bike and not familar with the power valve. What could I have missed. Went off the book and wondering how can I troubleshoot it? I really believe this to be the problem just need to know where to go from here. Thanks