Small Engines (Lawn Mowers, etc.): 4.5 briggs stops, spark plug, briggs

Question
I have a two year old Murray. It has a 4.5 Q engine. It acts like it has water in the gas. I have, over a three week time period cleaned and dried the tank twice and filled with new gas from the pump. I use the same gas in y other mower with no problems.
I prime it. It runs for about twenty seconds just fine, then quits. I have to leave it alone for about an hour and then it does the same thing.

Answer
 Hello Bill:

 When the Engine Stops; does it still fire the Spark Plug. If so; Clean and Overhaul the Carb. There's Trash in the Carb. All Ports and Passages need to be Blown out with High Pressure Air. Hope this Helps.

 Good Luck

 Respectfully

 John