ACF, I wouldn't necessarely count too much on a new plug as there could be an issue with the reed valve. The standard plug is crap but it is usable for a while, at least. If the engine starts and quits after a few seconds, it is, most likely, a problem with the fuel supply. If the carb is O.K., then there is only one other component, that could be the culprid: the reed valve.