I was on my way to Scotland, about 1994, when the RH350 (as it was in those days) suddenly saw fit to misfire and then stop. Diagnosis revealed that the ignition timing had indeed slipped. I retimed the bike, made sure the mag sprocket was good and tight this time, popped the bike into gear and set off - only for the timing to slip again. So I retimed it, and this time made very sure that both mag and cam sprocket were very tight. Put the bike into gear and got about 10 yards before it all went wrong again.
The armature shaft had sheared where it goes into the brass casting which houses the windings. I hope yours hasn't done the same, but its easy to test. If you can turn the points carrier by hand (not spanner, because if its ok, a spanner will do damage) but if you can turn it with your fingers you have a similar problem.
36 4G, 37 VH, 53 ex ISDT KHA (project), 54 KH(A), Healey 1000/4 (project)
Former Machine Registrar & Archivist, General Secretary and Single Spares Organiser (over a 25 year period).
Now Archivist once more - but not Machine Registrar.