Well, my '00 rm125 hasnt been having any power here lately, no jumpy power band, nothing-- so I rebuilt my top end, and while doing that found another problem, the plastic bushing in the power valve was not there, so i ordered that, got it on today, went to the track, and still not much power at all -- what could be going on here?
your power valve is stuck shut.
if you don't know what I'm talking about, go to a shop, or buy a service manual. Pretty easy to check and see if the valves are free and if the linkage is connected.