How longs it been since it was rebuilt?
Do a compression test and see where your at. I would bet its about ready for a rebuild. You probably have some worn rings and cylinder, and low compression. 2 strokes wear out, just the nature of the beast.
Low compression will hurt your low end, and make it hard to start, but top end will feel "ok" as its moving so fast it can build enough compression to pop the air/fuel mix.
Good luck. Check the compression and come back to us.