Thanks Mark, it sounds as if it is just a clearing exercise on the muffler. If the compression, mixture and spark are right, it can't form new carbon deposits, just burn old ones. I agree though that once the grass is short, you can't put a load on the engine and the exhaust won't be hot enough to burn some of the deposits in the muffler. Please let us know how the situation evolves. I think there are plenty of people who want to know more about the process of recovering a carboned-up engine.
