check for bad connections at distributor and ignition model,,where wires plug into each other ,,,the sockets can crack inside and cause arcking of the wires,,,we use to have to cut the old wire connectors and reconnect wire to wire getting rid of the bad connectors,,,this drove us nuts on a fleet of vans,,,,did the same thing you say,,,,crank and crank,,,,and every time you where ready to let go of the key it would run for that second,,,hope this helps

yes it will stay running ,i have been fighting a short in the purple wire a summer and right at the end of the year found it,,where it plugs into the mod it was not making good contact and the boat would miss like crazy,,sound like i still have a proublem,,can i buy a new wireing harness ??and all this should be fixed??