[Dick Boneske]

Did you have good vacuum before the carb rebuild? If so, there is likely something plugged in the idle circuit, probably the venturi cluster. Idle tubes, idle bypass restrictors, are the ones with small holes that could be plugged. If you give us the parameters of the engine--cam, C.R., cubic inches, etc., we can tell you what the idle circuit orifice sizes need to be. A moot point if it ran OK before the rebuild. PM if you need to.

Also, I've had low vacuum with a carb-to-manifold gasket with holes in it outside the two throttle bores. The base of the carb will not seal to the manifold with the "Chev" style gasket. You need to use a solid base gasket with only throttle bore holes and carb mount holes. As Kenth pointed out, the open or closed gasket makes no difference.