One thing that a few of my old cronies and myself years ago, did was not properly set the lean drop at idle. It can be hard on emissions carbs because of the sealed idle screws but it's a good place to start. If lean drop isnt set correctly you end up relying on the idle screw to keep it running at idle. This most times kicks the throttle plates open to far and ends up creating the rich condition through the idle circuit. Once i Iearned how to set mine my truck ran a ton better.. not sure if that's really the problem but it's an important adjustment. Also gonna want to check the secondary air door spring tension. If the secondaries come in too soon it will rich up.
