Small Engines (Lawn Mowers, etc.): lawnmower engine runs occassionally, brigss, starter fluid

Question
Hi, I have a Brigss & Stratton 20 HP 460777 engine on riding lawnmower. Changed sparkplugs, oil, air filter and gas filter.  It has a hard time cranking on, but when it does it runs fine. Maybe a little fast.  Problem is that it runs for about 15 minutes then it dies. Sometimes it willl start back up and run for another 20, other times I have to wait a full day for it to start up again.  Battery is OK.
Please help, grass is so tall I lost my kid for 2 days in it :-).

Answer
 Hello Jorge:

 Thats a Good One for me to Tell the Wife, Thanks LOL. From your Description you need to Check the Gas Tank Cap and Ensure it is Venting the Tank Properly. When the Problem Occurs, Check for Fire at the Plug. If there is Fire at the Plug, then Try to Start the Engine with Starter Fluid. If the Engine Starts and Quits, Then the Carburator needs Cleaning and Rebuilt. If No Fire at the Plug, then the Coil/Ignition Module/Igniter May be Bad. Im Leaning towards the Coil/Ignition Module/Igniter. Check the Compression Both when the Engine is Cold and Again when the Engine Quits. The Compression should be No Less Than 70psi. Hope this Helps. Let me know what Happens, Please. I really Enjoy knowing the Outcome. Thanks.

 Good Luck

 Respectfully

 John

 Hello Jorge:

 Clean and Rebuild the Carburator. Hope this Helps. Let me know what Happens, Please. I enjoy knowing the Outcome. Thanks.

 Good Luck

 Respectfully

 John