Troy-Bilt with Kohler won't stay primed

I have to pour a little gas in the carburetor to get it started. After it starts it is fine. It will run. If I turn it off and start it back up within 10 minutes or so it will start. If it sits longer than that it will not start. It's a Troy-bilt Super Bronco Hydrostatic with the Kohler KT735 engine.