I've built another set of factory E carbs for my 57 OD car. They idle @ 900 RPM's but if I push down on the primary throttle shaft level assembly it closes the secondary throttle shaft assembly and the engine will idle @ 500 RPM's. I just need to bump it and it stays down until I rev the engine and the idle is back up to 900. The fast idle cams and the idle screws are not in play and I've synchronized the linkage per the Ford guide book. As you can see by the photo @ 900 RPM's the linkage on both carbs secondary have enough movement to idle the engine @ 500 RPM's so the linkage is not binding. A light spring on the primary lever assembly would bring the idle down but this is a farmer fix. My question : Is vacuum suppose to keep the secondary plates closed until throttle acceleration? Any helpful suggestions would be appreciated. Philip in Ohio