[ted]

I'm assuming you have the staggered carbureter linkage where the car drives off of the front carb in low throttle situations and the carbs are installed backwards on the intake. Try closing the idle to almost "nill" on the rear carb with the idle mixture screws turned one turn out. You want the rear carb throttle plates almost fully closed but cracked open just enough that they will not stick. Then idle the engine off of the front carb and reset the front carb idle mixture screws for best idle and see if this cleans up the "richness".

If your linkage is such that both carbs are working simultaneously all the time, then disregard what I just said.