Knowing exactly which carb you have would help but here are some thoughts.  The engine is obviously too rich at idle and that could be the result of several different items.  Assuming that the float levels are correct in both ends of the carbureter, the simplest cause would be the idle rpm being set on the high side.  Second would be the idle mixture screws just being out too far.  If you can screw both idle mixture screws in completely and the engine still runs, then there’s likely too much idle transfer slot exposed below the throttle blades and that can be corrected several different ways.  Assuming it’s not a faulty or leaky gasket at the power valve causing the excess of fuel at idle, then opening up the secondary throttle blades some more will allow the primary blades to close an appropriate amount which in turn will decrease the amount of idle transfer slot that’s exposed.  Drilling a small hole in each primary throttle blade will also help to close these blades some more also but this should only be done once it’s determined that all else is well with the carburetor or general tuneup.  If this is a List #1848 carb, then the fix should be relatively simple.