I have a Toro zero turn Timesaver Mower with a Koeler Courage 20 hp engine that is several years old. It starts up and runs fine until you shut it down and it won't restart. If you let it cool down for an hour or so it will start up fine. I've changed the battery and the solinoid. When it's hot and you try to start it you can hear a slight ticking sound from the starter.
Sounds to me you might have a loose connection. Make sure that the starter and solenoid bolts are tight. Also check the the ground cable to the chassis is clean and tight.
