Water in the fuel is a possibility. Dump all the gas and fill it with new fuel from another can or source. If that fails to fix the problem you will have to do some testing.... Get a spark plug socket and be prepared to quickly remove the spark plug. Run it till it dies and pull the plug, lay it on the metal part of the engine while connected to the plug wire and get someone to pull the starter or try the electric start while you watch for a spark. If no spark then it is likely a heat related ignition coil failure. Before trying a new coil put a new plug in to be sure it isn't the culprit. The key here is getting it to fail before testing.