Finally, found the problem. Last thing I would have thought to look at. Someone had replaced the coil with a non B & S one, looks like a Honda. What was happening was when you throttled back towards idle the governor flag was catching on the corner of the coil preventing the throttle from coming back to idle, after trimming a small amount of plastic off of the inside of the governor flag the issue ceased to exist and it is now running properly. Who would have thought.
