The new spark plugs I ordered from eBay arrived today and I couldn’t resist plugging them in to see if they made a difference. They did!
£30 including postage, which is just a little bit less than Paddocks are selling them for (£40 for four). They arrived in the original boxes which had been opened, but clearly the plugs themselves are as good as new. The picture gives a clue as to why the boxes were opened!
Anyway, after fitting the military distributor the engine was running much better – idling smoothly at about half the revs and happily responding to rapid accelerator pumps. There was an occasional miss though and after a while it ended up running on three cylinders. The spark plugs I got with the distributor (from Sodbury) were pretty knackered and it turns out that this was the cause. As proved by the new plugs!
So, with a bit of luck the engine will now have the power it needs to get me to and from the next MOT failure!