Here are a couple of pictures showing some of the internal circuitry regarding the distributor vacuum for the Holley 4000 4V carbs.  I’ve included the secondary system page due to the internal circuitry for that system also interconnecting with the distributor vacuum signal.  The spark advance valve helps to balance the venturi boosted vacuum signal with the ported signal so that the ignition timing is appropriate to the amount of throttle being applied.
  

Lorena, Texas (South of Waco)

On the dual quad setups I simply stage the primary blades in both carbs equally at idle.  This is accomplished by completely closing the primary throttle blades and then opening the idle adjustment screws the same number of turns.  I typically start with two turns of idle adjustment on each carb and then with the engine hot and running, adjust both carbs equally either up or down for the desired idle.  I’ll add that I do the idle mixture screws the same for both carbs.  I do like the idea of using a Unisync to calibrate the carb idle though.

Lorena, Texas (South of Waco)

Thanks Ted
I'll look into that article
Great writeup Ted. Thanks a bunch.
What I'm trying to do is balance (2) 4bbl carbs. Maybe I'll look into the PVC
pipe to make an adapter for the Unisyn. 
The thing I was really wondering is how the vacuum works? As an example, at idle, then cruise, etc
Thanks again
Jim

Yep, it was for his dual quads on his Bird.
Thanks for the info.


Jim
Norfolk, VA

"MABLE"
1956 Thunderbird Green / Brown Interior (ZE-XG)

"MEAN GREEN"
1956 Mainline (FG-BE)

I’m guessing the intent is to use the Unisync for a dual quad setup.  In that case it should work just fine assuming you can seal off the whole top of the carb with the measuring unit.  I don’t see any advantage in using it for a single four barrel application though.

Lorena, Texas (South of Waco)

Curious things I have read about and wondered if it works. It seems like the question fits here.
In the Thunderbird Restoration Manual some guy made a "Unisyn" device for his E Bird.
It was a PVC pipe coupling that fit on the rim of the 4000. He then fitted an end cap with a hole to fit an air flow meter something like this.

Anybody do something like that and do you think it would work?
Thanks,


Jim
Norfolk, VA

"MABLE"
1956 Thunderbird Green / Brown Interior (ZE-XG)

"MEAN GREEN"
1956 Mainline (FG-BE)

The vacuum signal for the LOM distributor comes from only one side of the carburetor regardless if it’s a two barrel or a four barrel carb.  That distributor signal is a combination of staged and venturi vacuum.  Here’s the link to the article that goes into detail on how to convert the Holley 4000 (Teapot) L-O-M signal to a fully staged or ported signal for the ’57 and up distributors.  Looking around through the articles will also find the instructions on how to convert the '56 and older Holley three bolt two barrel carbs in a similar manner.
http://www.eatonbalancing.com/blog/2013/03/02/modifying-the-holley-teapot-four-barrel-carb-for-late-model-distributors/ 

Lorena, Texas (South of Waco)

Guys, I'd like to know if anyone has a clear understanding of the Vacuum supplied by the carburetor for the "Loadamatic"
distributor?
What I'm thinking is that I could tune the idle/airflow using those carb vacuum outlets. Mainly cuz I can't figure a way to use
a Unisyn due to the odd shape of the carb tops. Does this make any sense?
Like I could hook up a vacuum gauge to each carb and see what the difference in vacuum is and adjust accordingly. Those 
vacuum ports are not used on my engine.
Rereading this, I'm not sure my description is clear
Jim