I found an almost broken wire on the positive feed to the coils so I fixed that (it was one of those horrible blue connectors which cut the insulation) and fitted a new ignition unit. In 5 or 6 20 mile trips (I live on a small island) it has only cut out once so I'm hoping that was a one off. I've connected a light bulb to the coil feed so if that stays on when it next cuts out I'll know the switches are OK and that the problem must be the 49 year old coils.
Process of elimination.
John.
