Any place that has constant vacuum Usually on the back side at the base of the carb.
There should be a vacuum source on the carb above the throttle body that gives spark ported vacuum. You can connect a tube from this source to the distributor.
Your distributor needs vacuum to advance your timing during acceleration. That's why you hook up your line to the port that has no vacuum at idle. :O)
There should be two small and one large vacuum connection points on the front of the carb, hook it to one of the small ones, that will be for your vacuum advance. the big one is for crankcase ventilation. one of the smaller ports is manifold vacuum, the other is timed vacuum. they are not the same, but you will use one of these, usually the "timed" port.
vacuum lines,there are three one for each petcock and one for the vacuum advance, the two for the petcocks go to the carb boots, one on each side,and the one for the vacuum advance goes directly to the no. two carb.
Check your timing and your vacuum advance.
Look on the carb for a small vacuum source above the throttle body. You would want one that has no vacuum at idle.
It hooks up to the vacuum ports on the carb or intake.
If it is a point type distributor you will want to hook it to constant vacuum...somewhere on a port in the base plate. If it's HEI you'll want to hook it to one in the carb body. Something that has no vacuum at idle but pulls vacuum as you give it throttle.
It depends on the year of the car.....but if you are running HEI ignition (74 and later) it will run to the carb. It goes to a ported vacuum signal. You will find a ported vacuum on a fitting that is above the carb base plate. It should have no vacuum when the engine is idling but will have vacuum when you rev the engine.
It has to be hooked to a vacuum port that only has vacuum on it when you give it gas, That is called ported vacuum. If you look at the holly, you will see some small vacuum ports on it, start engine and witch ever one don't suck on your finger then that will be the 1 you hook it to. Then plug the rest if you don't need them for something else.
Connect the line to a source that is above the throttle body on the carb. It should be a source that has no vacuum at idle.