You are not telling us what is happening, only the engine dies. Will it crank, slow, fast, kick back, not fire, try to hit. What does it do when you stop, chug, load up, rpm just start dropping. It is like hunting. You have to turn all your senses on to what is around you, not just rely on one sense. To throw some guesses out there, Is your gas tank vented, your gas line too close to engine heat, ie exhaust, coil getting too hot, etc. I am sure it is something simple, but you really need to get your mind in gear, not just the engine quits. Do you try to give it some gas, or just let it die? Sometimes the accel pump will keep it running, this would indicate a possible fuel problem. The carb could be getting too hot and perking the gasoline. It's just small stuff for the old guys. Unless you had some indications of over heating, changing a thermostat would be the last thing on the list.