68 camaro 327, Still has the original intake also with the 2 barrel rochester. Cannot get it to run right, seems like a vacuum leak. It will not idle, until you put your hand slightly over the carb. The idle mixture screws do not do anything as well. I rebuilt the carb last night, now it will idle at like 500 rpm barely, at like 5hg of vac until you put your hand over the carb slightly then the vacuum goes right to 22" hg and idles great... Any thoughts?

 

Could be the throttle valve is not closing properly or that the idle speed screw is maladjusted. The idle mixture screws do just what their name says, they are not for controlling idle speed.

 

Spray some carb cleaner around the base of the carb and at the interface between the intake and heads and see if the idle picks up. Putting your hand over the top is acting like a choke blade which richens the mixture. You must be running dead lean.