Re: Uncle Don
Yeah, if it doesn't ping on light acceleration, then full manifold on the vac advance should work, as the manifold vac will go down at high RPM and heavy load (wide throttle opening). I think they usually set them up to have mostly vac advance at idle/light load, then as RPM would increase the mechanical advance would start to come into play, and at high RPM would be mostly mechanical as the vac advance would drop off.
Playing around years ago, I temporarily turned an Olds 455 into a real slow-rev'er by plugging the hose to the vac advance (so only the mechanical was left). When you would get on it, it would rev up slow. The vac advance can give a quick response to throttle opening when it's on the venturi port, but mechanical advance only increases as RPM increases (the two tied together mechanically through the advance weights and springs turning the breaker plate ahead in time).
It's been almost 30 years since I played around with changing weights and springs on mechanical advance!
On the Bronco, maybe they were trying to get some sort of mixture between ported and manifold vac. Check valves of the early 80's Fords were about an inch in diameter, but a "Vent" gizmo was black rubber, about 1/2 inch in diameter, maybe 1 inch or so long, with a little screen in the end of the cylinder. I had an '82 302 full-size Ford car that had an unbelievable assortment of check valves, restrictors, 3-way vacuum gizmo's, miles of vacuum tubing, etc. on it. All that stuff and the V-V carb disappeared with Fuel Injection.
So is your Bronc OK now? Or did you mean that on manifold vac it behaved the best, but still pinged at higher RPM?