Model #20371 FWD with Kohler 6.75 cc starts first time every time, but when I stop for a 15-30 minute break (it's a big yard) the mower won't start back up. I clean the spark plug, open the gas cap, but nothing works. An hour to 90 minutes later it starts right up again on first try. Theories anyone? Yeah, I know, don't take a break.....that's my only current solution!