My /6 is running rich

For sure. I know of 3 different 1 bbl carbs used, and those varied considerably from 1962 to 1976. Post photos. If running rich, your mileage will be bad. Besides the carb, it could be a non-functioning cylinder (no spark or no compression) passing raw fuel. If so, the spark plug will look real clean. Could also be running lean at idle so it is mis-firing, which also passes raw gas.