I'm no two stroke guru, but I've owned a few. Usually when they're rich up top, they cut out, almost like a rev limiter. It's real noticeable and not just a decrease in power. It's a choppy type of running.
If the power is backing off up top, but otherwise running smooth (ish), it may be lean. It could be something simple as a restricted fuel filter or fuel cap vent, to something else that'll need a more in-depth look.
Running lean on a two stroke means it's also not getting enough oil. I have seized one up from lack of oil, and been nervous about it ever since.
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