The actual model # would be a 5 or 6 digit # with a code next to it. It would be stamped in the metal shroud that covers the engine- sometimes above the muffler on the heat shield and sometimes above the spark plug. If, however this is a carb on tank model- the most likely cause would a fatigued diaphragm.

The symptoms are from a rich condition - too much fuel. But, the same things can be caused by using improper or old fuel. Most likely you need to work on the carburetor as tomplum stated.

Generic advice. Before tearing into the carb, try this. Drain the fuel. Add a few OZ of B12 Chemtool or even several good shots of spray carb cleaner Put in enough fresh gas to run the engine to operating temps. Get it running and let it run. If it cleans out, great. If it doesnt,you will have to take the carb apart to clean it.

Hi All,
I took the carburetor off today, as per the instructions in a video I saw on the net. There wasn't anything obviously wrong, according to my untrained eye, so I cleaned the filters and reassembled it. Now it works fine.
Thank you all for your help.
...... john