Hi Bob,
Did you pull your plugs?
Next time this happens, immediately shut down and pull the plugs. If they are all black and sooted, then you will know why it is running rough. Then do what I did.... Let it run at 4000rpm for a few minutes, and then drop to idle and shut down.
Also - Check your choke linkages. I had an issue once where the choke on one side would not release at the carb. So the choke was essentially on all the time. Sorted that out and all good.
Something to think about.
