First check the pipe where it goes into the engine. They come stock with a spacer the reduces power remove it if it's in there. There really ins't a rev limiter on the pw other than the screw in the throttle. You can gain a few rpm by disconnecting the start/run switch. Simple as unpluging the wires that run from the killk switch. Not sure which ones.
on a newer bike there is a plug that only has the 2 wires that go to the start run portion of the switch. Not sure which ones it is on the older bikes. you can simply trace the off wire that grounds the ignition and clip the other 2 wires. This will make the bike start no matter which posistion the switch is in, either start or run. The bike will still die when switched to off. This disables the retard function of the ignition givving a few more revs up top. slightly noticable on the top end.
had another guy mention that the rev limiter is a black item resembling a diode under the seat. I never checked udner there on the older bikes. apparently it has a connecter there you can disconnect and do the same thing as the newer bikes up near the bars. So look for it under the seat.