I have a '71 40 with the stock engine, I changed the old carb with one from a 78. The butterfly valves dont want to close all the way, I checked for tension in the accelerator cable and there is none, and I have put a reletavely strong return spring in also. I can pull it closed with my hands, but when I let go it opens right back up. I have completely desmogged the engine, and only have one vaccum line running to the brake booster, and one to the valve cover. Any help would be greatly appreciated.