How old is the battery? What condition is it in? What kind of ignition? What kind of engine? What kind of plug, including the part number? Did the engine have the right plug to begin with? Just because the manufacturer provided the plug does not mean it was the right one. Was the plug correctly gapped? Was the engine tuned? If so, is the engine lean and shutting down because it's too hot? Changing the battery gives the engine time to cool off.... Do you have the ignition mounted right behind the engine or in line with the hot exhaust gasses?

You did not provide anywhere near enough info to begin providing assistance.