I’ll add a photo to help clarify... I just used a carb kit to rebuild a 2 barrel Carter carb for my 1971 318 Duster. I cleaned everything a well as I could using a carb cleaner, rags, etc. I noticed that the vacuum piston plate assembly wasn’t moving freely when re-assembled. It moved fine before the retaining screw was added - but intermittently sticks with the retaining screw added. I installed the carb and wasn’t too surprised when it didn’t idle well. Couldn’t make any improvement with idle mixture screws. The car starts great - but idle is not good. It runs ok at higher rpm and takes gas well when throttle is opened. Any suggestions on how to get this piston to move properly?