Head gasket was always an unlikely solution; wrong symptom. The symptom is possible for a coil but it wouldn't be the first place I'd look unless that engine is known to have that problem. Coils sometimes have intermittent failures but more often they just quit once and for all. Fuel sounds more likely, and you can check that fairly easily. Will it restart immediately after it quits, or do you have to wait a while? If you have to wait a while, you can try to start it immediately after it quits by squirting some fuel into the carburetor air intake (with air cleaner removed) immediately after it stops, then cranking it. Don't stand in front of the carburetor air intake when you do this, in case it spits. If it isn't that, I suspect you'll have to do the standard series of diagnostic tests, but I see Bruce is on line and he may have seen this problem before. The quickest way to fix these things is to ask Bruce.
