I'd gone through the ignition and rechecked the carbs to no avail. I was about to start tearing my hair out when I noticed a slight blow at the head gasket joint just between 2 & 3 cylinders. Saturday saw me changing the head gasket and it was the cause of the problem as the car ran as well as ever but (there's always a but) not for long.
A misfire came into the mix. Loss of power and rough running weren't what I wanted. As I'd had the carbs off, this was my starting point. I checked everything without success.
Work got in the way a little and I had a couple of days not being able to drive as I would have liked to. Having found nothing amiss with the carbs, I decided to try a new set of plugs. I'd obviously got the mixture right as the plugs were a nice tan colour, but No.4 was wet. Hmm, that's not firing. New plugs didn't make any difference. I had a spare set of plug leads at work so this morning I set to to change them. I pulled No.4 lead off the plug and it came off the distributor cap as well. I don't think it was supposed to do that.
Once properly reconnected all was well again and the car ran fine. I don't know how long that lead had been loose in the cap but I don't think it was the cause of my original problem.
It must have been my lucky week, two problems for the price of one.