Son gave me an old 3.9 Merc that didn't run and seemed to be on it's way to seizing (very hard to turn over). Also lower unit had big crack which I had welded. I put some penetrating oil in the spark plug hole and it loosened up. I hooked up the fuel line and shot a bit of WD40 in the carb and yanked. There was a pretty good explosion and fire but motor was running and burning at the same time. I got hose disconnected and fire out. Now no spark. Tried to pull the flywheel with wheel puller. It won't budge. Any hope for it or just scrap it?