Slant Six Dead Spot

Ok then, explain this. How can six different carburetors of varying cfm, manufacturer, and style, mounted differently using new gaskets, all pulling good vacuum produce the exact same dead spot that can only be helped by delaying the vacuum signal to the distributor? How can they all have the identical skewed ratios of air to fuel?

The Carters I had ran lean and the Holleys and Motorcrafts run rich, but they all had this constant problem.

I have been all over this engine with a can of starting fluid, checked every vacuum port, there is no vacuum leak.

This engine is NOT running lean with this set up. I don't have to stick a sniffer on an exhaust pipe to know how it is running. The plugs are black, a rich solid black, not white and the exhaust reeks of and spews out raw gasoline. The engine runs out just fine, and I can't get it to spark knock, and that's not for a lack of trying.

Sorry, to be "hard-headed" but to fix a problem you have to narrow down the factors, most of these steps I have already taken at least once. Granted I don't know what the problem is, but I do know what it isn't. I have been through all the easy "solutions" if something simple would have fixed it, something trivial, I wouldn't be here.

Thank you, jdeval. Yes the black smoke is a sign of poor combustion, but it is because the engine is getting more fuel than it can properly combust, this wasn't an issue with the other five carburetors.