Hello!  I have a D code 57 with a factory Carter AFB carb. car runs great until after I open up the secondaries! they hang open and the car idles around 1500 RPM. if i remove the rod to the vacuum diaphragm the back butterflies close and the car idles normal. the diaphragm is currently unhooked so i can drive the car. all of the linkage is free, nothing binds up. i have spent several hours trying to figure out this problem. also, if i shut the car off after the secondaries hang open i can watch the diaphragm slowly release and the secondaries will eventually close. i have tried different springs and everything else i can think of. i have little experience with these carters. thanks! Marlon....