1977 Corvette 350 Carburetor Has High Idle

[jberenyi]

Just cleaned and rebuilt the OEM carb for this Vette.  Casting number is 17057584 which stipulates high altitude.  I'm at 4500 ft here in Utah too.  The main jet size is .071 but the specs say it should be .072.  Not sure if this is the problem causing a high idle.  I'd like to get the idle down to 600 to 650 rpm but can only get down to 800 rpm with mixture screws set at about 2.5 to 3 turns out.  At this many turns the idle is fine.  At 1.5 to 2 turns she's rough idle at 600 rpm.  What could be the problem?

[Cliff Ruggles]

Vacuum leak someplace will cause this. 

Too much timing at idle can also cause loss of control or idle too high even with the speed screw backed clear out.......