It wasn't the lack of a heat shield!

[Mckorkins]

I think I've found the cause of the occasional misfire on my moggie. Sometime ago it was changed from positive earth to negative earth and the coil polarity wasn't switched at the same time. The old coil was one with the terminals marked CB (contact breaker) and PW (power switch) and they were still connected as it said on the tin! Someone did helpfully suggest it might be the coil breaking down, but not reverse polarity. Whether that was the cause or not, I can't be certain, but the car ran beautifully today on our picnic run to the Quantock Hills with a new coil marked '+' & '-' . The '-' terminal being connected to the contact breakers. So there!

[bmcecosse]

Now put the old coil back on -and CONNECT IT PROPERLY!

[Mckorkins]

No, it's now in the boot as a spare!