This morning I was having the same problem with my Model "C". I removed and cleaned the carb, cleaned the inline filter and cleaned the tank out as much as I could, and drained it. In doing so I found that the tank had a lot of water in the gas apparently due to the heavy humidity lately. Once I put clean gas back in I added a bottle of Gas Dryer and it now purrs like a kitten. No more water in the gas.
Good Luck !