I would look into two things, one is jetting, a rich main will act like a rev limiter but sputter more when rich. The other is what pipe you have. Because you can control your RPM's with a pipe I haven't seen a 2 stroke CDI box to actually have a rev limiter. (Could be wrong though)
Different pipes rev differently, this is due to the leading taper. When you hit the pipe limit though it is like you just turned off the bike or started pushing the kill switch while in gear, far more significant change in my experience than being rich on the main. I recently had a Honda that the stock pipe on it limited me to about 7500-8000 RPM's, I changed the pipe to a FMF desert pipe and then I could rev to 9000 RPM's. (500cc's didn't like going much above that without some work.)