Right then.
I made a list of things to check and had a really good poke around under the bonnet this morning. Here's what I found:
Spark plugs were sooty, notably those from cylinders 2&3, so I cleaned them all and will reset the mixture next time there's a chance for a good run. Otherwise they were bone dry, with no sign of oil.
The points were rather below the correct clearence, so were cleaned, reset and the timing checked. Rotor and cap were cleaned thoroughly with lighter fluid and allowed to dry well...
I went through the coil & distributor spade connections, but also found that the connections in the fuse box were not very clean. Although they measured OK with the multimeter, I pulled all the spade connectors & cleaned significant deposits off all the tabs. This included the interconnections that the fuse box provides (separately) for the brown circuit and white circuit distributions.
Carburetors were firmly mounted and had free moving pistons, throttles and choke mechanisms. Manifold was firm on the cylinder head, but the exhaust system to exhaust manifold union needed attention. One of the brass nuts was missing and the other five were barely tight, so I wonder about leakage here perhaps contributing to running problems.
After all this fiddling, the car started and ran nicely, though it was already quite warm outside - being mid morning by the time I turned the key. I need to do a better cold start test, but fingers crossed, things are improved.
Cheers,
Ed
I want my MGB