Does the engine start back up right away or do you have to wait until it cools down to restart? If you must wait I suspect either an ignition or fuel problem. Next time it happens check to see if you have spark at the plugs. No spark means you probably have an ignition module or coil problem. If you have spark remove the gas cap, wait a minute, then try to start. If it starts, the vent in the cap is plugged causing a vacuum in the tank. Report back what you find. At this time I cannot post a manual link, but you can go to my mower parts com and get a service manual for you engine.
PS: spark plug gap should be .030".