Using manifold vac will help your carb run right. With manifold vac hooked up, your idle increases and then you can turn it back down and get your carb idling on the idle circuit and not the smoky black power circuit. It all has to do with the transition slot.
There's a section in here about that.
http://www.crankshaftcoalition.com/w...EI_distributor
It talks about a holley but yours is the same.