Small Engines (Lawn Mowers, etc.): Tractor wont start and carburator floods, hp tractor, carburator

Question
I have a Sears 19 1/2 hp tractor with B/S Model 42E707 engine, 3 years old. Ran fine first time used in spring. Second time ran for about 15 seconds then would not start again and had gas in air cleaner after cranking. Changed plugs and fuel filter and, if engine started, surged except on minimum throttle. Had carburator cleaned I was told carburator fine grit in ports. I was also nothing gets through fuel filter. Filled tank with new fuel. Engine ran okay for 2 or 3 cuttings then started cycle again with running for 15 seconds then would not start again and had gas in air cleaner after cranking. Had carburator cleaned for second time. Engine ran for 1/2 hour, I stopped engine then tried to restart engine. Engine started and surged except on minimum throttle. Flushed out gas tank, replaced fuel filter again, and rechecked plugs. Engine ran for about 15 seconds then would not start again and had gas in air cleaner after cranking. I know carburator probably needs to be cleaned again. Asked at shop where carburator cleaned what to do to prevent this. Never received a decent answer. Do you have any thoughts on how to prevent this and keep engine running?

Answer
Hi Gary,

You will need to determine if the problem is a lack of spark or a lack of fuel flow.  Right after it quits, remove the spark plug, reconnect the wire and lay it against the engine head.  Pull the engine over and watch for spark at the plug's electrode.

If good, then try to start it while squirting fuel or starting fluid into the carb intake.  If it starts and you can keep it running by adding fuel, then the carb most likely still has dirt, debris or gummed fuel inside.   
Another possibility if the problem is fuel related: Check the gas cap to make sure it is venting and not causing a vacuum in the tank.

Let me know how you make out.
Michael