My Craftsman Riding tractor mower has been working fine until yesterday when after mower was running about 5 to 10 minutes it started stalling. Choke would get it to keep running until throttle moved back to run and it would stall. I pushed back to garage and after I was able to restart and it would run like nothing wrong for a couple of minutes till would get heated back up. What could be causing this to start stalling. I checked air filter and cleaned this.