1978 Ford Bronco burning rich

There is also an air-fuel mixture screw at the base of the carburetor--this should be run in until it gently seats, then backed out 2 and 1/2 full rotations. I assume you have installed new spark plugs and cleaned cap/rotor as well as checked timing--all these can cause a rich condition as well. Be sure to grasp the throttle shaft where it goes through the carburetor and wiggle to check for free play--on older carburetors, the brass bushings wear out.