My bike runs good and crisp, right until you get to the upper RPMS. Then it sounds like it is bogging and sputters. Plug looks perfect. It does not have a power valve. Of corse,,it just started doing this after I put a FMF pipe on it. I put the needle where FMF suggested and it was worse. I moved it back,,,still same problem. If the plug looked bad, I could understand, but it looks perfect..nice and chocolate brown. Any suggestions??