One thing that might be causing the carb to run rich is the float. Sometimes the float(originally made of brass) starts to leak which allows the float to sink lower and lower until it causes the needle valve to allow more fuel to flow into the manifold than is necesary. You might also check the float setting, if the setting is wrong it can cause the same problem. O'reilly's still has some floats for the old carburetors and they are very reasonably priced.