Small Engines (Lawn Mowers, etc.): trouble, carborator, liquid cool

Question
I have a kawasaki 20hp liquid cool on a gravely promaster 200. It has been giving me trouble for some time now. It starts and runs for about 30 minutes and then stops like it is running out of gas. I try to start it again and it starts but shuts down right away. Now it don't start at all. I changed the carborator and it stills does the same crap. I think it might be one of the coils because I checked for fire and it only has fire on one side. Please help.  Thanks

Answer
 Hello Heath:

 You are Correct. One of the Coils is Bad. The Engine Heat After 30min will Open the Coil and it Will Not Fire. After it Cools the Open Closes and it will Fire Again. Run the Engine Until it Quits and Check for Fire Right Then. Be Carefull HOT ENGINE. The Coil is Gapped at .020in from the Flywheel. Hope this Helps. I am Here if you Require more Assistance. Thanks.

 Good Luck

 Respectfully

 John