....should the vacuum line be hooked up to manifold vacuum or venturi vacuum?
See Mike's explanation above.
As far as I can tell, there is no hook up on the stock Zenith or aftermarket Weber carbs for venturi vacuum. There are hook ups for manifold vacuum either directly into the intake manifold or at the carb above the throttle plates. As Mike indicates, the later is called ported vacuum but is exactly the same as manifold vacuum when the throttle plates start to open and uncover the port.
The choice is essentially to hook up the dizzy to the vacuum connection that gives the dizzy vacuum at idle (manifold) or not at idle (ported). With all other vacuum conditions produced by the engine, both will be doing exactly the same thing....that is advancing the timing at high vacuum conditions...primarily light throttle cruise.
I hook the dizzy advance at the manifold (stock dizzy). The engine is happiest at idle with the timing advanced. The idle speed increases as soon as you plug in that advance hose with no change in the throttle setting. Of course you have to time the engine with the hose to the manifold disconnected and plugged (you don't have to do this if you are using ported vacuum since the port is not uncovered at idle and no vacuum is going to the dizzy) and you have to reset the idle speed when you reconnect the hose after timing the dizzy.
If you are using a stock dizzy with two connections at the distributor vacuum canister, hook to the bottom (pyramid shaped side) of the canister. No connection on the other (top side) canister connection. Ported vacuum connections at the carbs should be plugged.
