Michael;

Thanks for the explanations...I did have a couple of questions and points which I couldn't get over, and ask that you elaborate on...

"when the throttle is opened, manifold vacuum drops essentially to zero, and the vacuum advance drops out entirely" ...I would say that is only if the Throttle is quickly opened to WOT (racing)...more realistically in real-world traffic, it is slowly opened, so the vacuum dropping is more a slow, linear action which the slow mechanical system can keep up with...

"At idle, the engine needs additional spark advance in order to fire that lean, diluted mixture earlier...." ...agreed on the timing, but we also go to great lengths to assure the Idle mixture is not lean...Colortunes, Exhaust Gas Analyzers, Lambda sensors on the later cars, carb lifting pins and noting the idle response, and adjusting the Idle mixture to be "just right"...

The article looks like it was more generic, written for American iron (a lot of which is certainly applicable)...but many of our cars came with Cent Adv only and didn't even come with Vac Advance...and some of the later ones even with the dreaded Vac Retard. Can you elaborate on how these systems play together, and action of ignition and engines of these configurations...

Thanks again for sharing you expertise!