If it is a 390 you can still jet down. Many things can make a carb too rich but to me it sounds like your fuel level is set to high or it creeps up at idle,that would either be caused by a bad float valve or maybe the o-ring on the float valve is bad. You can check this by removing the the plugs on the sides of the bowls(opposite side of linkage) with a standard screwdriver. Next start engine, if you see fuel run out then shut it off imediatly, if not then let it idle a few minutes and watch to make sure the fuel stays below the holes and is not creeping up slowly. Good luck.
