I'm pretty sure its not the Vacuum Advance as the problem existed with a faulty VA that wasn't sucking at all. It existed with the VA removed and the vacuum line plugged. And it's still the same with the repaired VA that works.
The spark plugs are grey/white
I think the mechanical advance is working because it moves the distributor when I rev it, but I'm not sure how many degrees.
The problem exists only when the engine is struggling going uphill, so not necessarily at high revs, but while doing about 30 mph.
I haven't had time to test if it's fuel related or not. Thats the next plan.
Then I'll look at getting some of the gunk out of the combustion chambers
