Thanks for all the helpful suggestions. I did the following to get the job done.
Removed the spark plugs. Front two were sooty, rears were looking lean. A compression test yielded readings of 75lbs on all four cylinders, so no valve/ring/piston problems.
I soldered, [not soddered] the terminals on the plug leads, as one came adrift while removing the plugs.
I checked the wiring/plugs/timer again and found nothing amiss.
I removed the inlet manifold and inspected the gaskets for leakage. The front port had a gland ring fitted, the rear did not. I cut two new gasket rings and re-installed the manifold with two glands and exhaust sealant either side of the gaskets.
Once I remembered to turn the ignition key on, it started right up on the hand crank and ran evenly on all four!
The carb still needs a new throttle shaft and plate, as I can't get anything like an even idle speed.
What I don't know is what I fixed. I would have thought that a manifold leak at the front would have meant a lean mixture on the front two pots. I had that on the rear two, going on the appearance of the plugs. I guess I'll just have to let the cantankerous old tart have her secrets and just enjoy having her behave.
Thanks guys.
Allan from down under.
PS. Even spellcheck doesn't recognise sodder!
Excellent!
Congrats. I enjoyed following your thread
Allan, you said the gland ring was missing on the rear port. That would make the rear run lean and the fronts rich. The mixture screw if adjusted would have been a compromise between the 2 sets of cylinders. Sounds to me that you figured it out. Make sure to readjust the mixture screw.