After you start your generator and it warms up, if you put no load on it, it should idle down. Once you put a load on it, it should speed up to handle that load. I would try putting load on it, such as your AC and see if it stays running. If it then dies when taking the load back off, that would indicate it is running at too high of RPM with no load. I had that happen to mine and it was caused by the throttle linkage being jammed with debris...grass, shredded paper towels and plastic bags...brought into the compartment by mice. It is worth investigating to see if something is not allowing it to idle down.
Just a thought.
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