And I should add one way to help chase down a vacuum leak (won't work in some cases) is to get a propane torch, don't light it but open the valve slightly and pass it over possible areas of concern. Throttle shaft exits, where carb attaches to manifold, where manifold attaches to head...places like that. Hear the idle speed increase? There's your leak. Or at least there's one of them. There could be more.
