Small Engines (Lawn Mowers, etc.): lawnmower engine, hp briggs, self propelled lawnmower

Question
I have a 6.5 hp briggs and stratten engine on our 3 year old self propelled lawnmower.  The mower will start and run rough for awhile and then begin missing and loosing power.  The spark plug is removed and it becomes black. After cleaning the plug the mower will run better for awile but far from perfect. I have changed the air cleaner and replaced the spark plug.  What might be causing this problem? Coil or carburator?

Answer
Hey Howard,
You probably have a gummed up carburetor and it should be cleaned. Soak the carb is gasoline for about 2 hours. Then clean the carb out with pipe cleaner or compressed air. Feed air or pipe cleaner through every hole and see how it starts. Hope this helps. Let me know how it works out.