Small Engines (Lawn Mowers, etc.): push lawnmower stalls frequently, briggs stratton, hp briggs

Question
I have a Craftsman 6.5 hp (Briggs & Stratton), 21", gear drive, self-propelled mower that starts and runs good for about 10 min or so, then starts losing power and stalls out.... then it restarts and runs for a while and does the same thing.  It doesn't seem like it is always the same amount of time and sometimes I can keep it running through the weak part, but then it dies out again a few minutes later.  If I am alright with starting it about 18 times, I can actually mow my lawn.

Any ideas what I can do to fix this?

Answer
Sounds like a dirty fuel system.  Clean the fuel cap vent, fuel tank and filter and fuel line.  Remove the air filter and remove the carburetor.  Discard all gaskets and air  filter.  Take the carb apart and clean with hot soapy water.  If you have an air compressor or canned air, used to clean the computer, blow it out.  If you have carb cleaner spray it through all the passages.  Install a new needle and seat and all new gaskets and bowl O ring. Reassemble using all new gaskets and a new air filter.  Put fresh fuel in the tank.  Now is the time to change the oil, sharpen the blade, etc.