Freq2002,
Beautiful engine compartment. Have you thought about the coil. Is your rig positive ground? Is the coil wired for your polarity.
While black smoke and chugging point toward the carburetor, if the ignition system is failing, or the points aren't allowing the coil to fully saturate, your going to get incomplete combustion.
A failing coil, or valves that are too tight would be on the list of things to check. The power valve must have the ability to sense engine vacuum....is the base gasket installed properly.
I don't think the heat riser would have much bearing on your problem. It looks like you have a Hydrovac. Is the vacuum line from the manifold snug and leak free?
Stuart
