Leon,

Me thinks you are too lean on the center carb because somewhere above I saw you had the air fuel screw 3 turns out. As you know you want no more than 1+1/2. Richen up the idle fuel delevery some and try to readjust back to 1+1/2. Keep going til you do. Just like Holley Webers richen up the ilde circuit. Get them end carbs to completely close on idle.