My Vanguard V twin began searching, racing up and coasting down, racing up and coasting down. Like the acceleration jets were fine but the idle jet was plugged. Not so. It has a fuel solenoid on the side of the carb that pulls open when you turn the key on and of course closed when you shut the key off. I guess so it won't diesel or let gas continue to flow while it is coasting off. Apparently when the engine gets hot it gets weak or fails to work. The engine thinks you are shutting it off but is still working so the governor kicks in to bring it back up to speed then dies again and so on. The fix was removing the solenoid cutting the solenoid pin off with dikes and replacing it. Runs like a clock now. Another piece of EPA bull crap defeated. FYI.