Jerry, you say it is running rich when it runs. Can you tell us how you determined that? It is almost impossible in my experience to get an engine to idle well if the idle jets are set to rich. If it is really rich, like black smoke at idle, that has to be float or need and seat problems. The discolored tailpipes are most likely due to water, just normal condensation as a result of never getting the pipes hot enough to dry them out.
If you do decide to disable one carb, be sure to run the idle speed screw out far enough to completely close the butterfly and seat the idle fuel screw.
The low vacuum could be any number of things, retarded timing, couple with butterflies to far open will do it. So will tight valves.
I would double check float levels and accelerator pump function first. Set idle fuel mix screws and close the idle speed setting. Then set timing as far advanced as possible and still start without kickback. Then start it and turn the idle speed screws in a little at a time, on both carbs until it will run. Then warm it up and back the idle screw on one carb down until it slows, move to the other carb. Keep that up until you reach the speed you want, probably around 650-700. Then adjust the mixture That will probable require a tweak of the speed again. Then back to the timing. Keep up this dance until you get were you need to be.
Let us know how it works out.
