Small Engines (Lawn Mowers, etc.): lawn mower surging, water in the fuel, dirty fuel

Question
I have a five year old Murray lawn mower with B&S 4 h.p. engine that has suddenly begun surging.  I can smell unburned fuel and the mower is using much more fuel than previously.  Just prior to the tank running out of fuel, the surging stops and the engine begins to increase speed.  

What do you think is the problem?

Answer
Surging is caused by just a few things.. Dirty fuel or water in the fuel.  Running rich which would indicate a dirty, oily or plugged air filter.  A plugged fuel cap vent.  Fuel line restriction, dirt in the carburetor or a failed groomer. Look for the easiest first.  Work from the outside in.  First check the cap them the fuel then the air filter then the fuel line then the carb then the governor.  Hope this helps you find it.