It's usually the mag failing if they won't start hot, the later mags are bad for the bakelite shorting out when hot, I've got 5 distributer caps and they are all junk, expensive scrap. The early mags must have a different bakelite recipe and don't seem to suffer from that problem, although I did turn it on to petrol once for a hot restart, and the petrol vaporised in the float bowl and sprayed out all over the place. Bit of a fire hazard! Didn't do that again!