If he has 4 throttle plates with individual runners, and vacuum coincides with the opening of the intake valve, I'm quite sure he'll need to take vacuum from all 4 carbs/throttles. Otherwise won't the dizzy see "pulses" of vacuum?

It would work if all four carbs can see the same vacuum signal. By that i mean that an isolated runner manifold design would be a problem, & linking to all four carbs wiuld be best, but if all the runners are kinked with a balance pipe, you should be able to get away with one.

Anyone else care to contribute?

So hooking it up to a ported vacuum fitting ONE of the carbs would be okay then? (there's 4)

Ddgonzal is, as usual, 100% correct.

If you draw vacuum for the distributer direct from the manifold, you get full vacuum advance at idle, assuming that it actually develops vacuum at idle. [I dont know your cam specs.] This is BAD

If this is a road engine, then you will want to have the vacuum advance wotking in an attempt to increase operational efficiencies at part throttle, like in cruise mode. The ONLY way to get the correct vacuum signal is to use the ported vacuum fitting on the / a carb.[It does have one doesn't it?]

This port is just upstream of the throttle plate, so that when the plate is at idle, this port sees NO vacuum at all. As the throttle is opened, as in full throttle, there isn't enough vacuum to suck fizzy drink up a straw, so you get mechanical advance only.
Once you are up to cruise speed, the throttle is reduced & this port can see some suction. This results in more acvance & increased eficiencies. Read this as, "improved fuel consumption figures" which is what you want when just cruisin'
Stab the pedal, throtle opens, vacuum vanishes & ignition timing reverts to centrifugal control only, It works a treat, but manifold vacuum at idle messes with your traffic driveability & thats a pain.
Chris

vaccuum advance does a lot. This has been discussed several times in this forum.

Mechanical advance comes into play at higher revs. Vaccuum advance does nothing at full throttle. But at part throttle it advances the timing. You do want the most timing, don't you?

Thanks for all the replies. If it doesn't do much except for idle/near idle advance then it'll probably be okay for now. I'll have to research where I can send the dizzy in Japan to get it worked out. What plugs are you guys with high compression, sidedrafts, cam and headwork running?

From my experience with side draught carbs. I have never run vacuum advance to the dizzy. Dial in your dizzy to required specs, The only suggestion i could make, well two suggestions is 1.re-graph the dizzy and 2. modify the springs / weights of the mechanical advance to match your modified CAM.
To my understanding vacuum advance essentially only plays part during idle and near idle until mechanical advance takes over.

Cheers,

Benny

no id think that would be much harder than necessary, it only needs one tap appropriatly placed before the seperation to each cylinder

Quote:
Tap into each runner and install a vacuum canister that all 4 lines run into. Then run a single line from the canister to your dizzy.

oh yeah congrats on getting it running!!!