I am familiar with the uni-syn, but can you synchronize two AFB-style carbs on a low rise inline manifold by using a manometer or vacuum gauge on the vacuum port on each carb? Would you actually be measuring the flow for that carb or really just reading the manifold vacuum overall?
I don't think you can synchronize dual quads that way. You can't use manifold vacuum, because it is the same everywhere in the manifold, it doesn't matter how the individual carbs are set. And ported vacuum won't tell you what is happening at idle. I'd do one carb at a time. Back the idle speed off on one carb, then set the idle speed where you want it on the first carb; then dial in the fuel mixture screws (screw it In/Out to achieve the highest vacuum draw, then screw it in to achieve a 20rpm drop on the tach (lean roll). Do one side then the other, then reset the idle speed where you want it). After you get the first carb dialed in, do the same to the other. Screw the idle adjustment in just until RPM increase slightly, then back it off just slightly (till the rpms drop back to where they were), then do the fuel mixture screws the same way as the first carb. Plan on spending some quality time with it, developing a feel for how the carbs respond to the adjustments, using your ears as much as your eyes. I first learned to adjust carbs watching my dad, who did it all by ear. I next learned how to do it using a tach, and later added a vacuum gauge to the process.
Once upon a time........................there WAS a uni-syn that was sufficiently large to cover the AFB air intake. One had to cut a piece of water pipe to clear the air cleaner "ears". I haven't seen one for sale in 25 years. I do have one from yesteryear. Actually, it will clear the small intake AFB and WCFB; you have to cut the water pipe for the large intake: http://www.thecarburetorshop.com/Uni-syn_4-bar_1.jpg Jon.
Amazing how the old guys did it My dad did the adjust it by ear thing too, even for timing. Used a glass of water on the fender. Used to tell me "watch the ripples in the water, it will tell you more then your ears can hear" then he would adjust until the water was the smoothest AND sounded right. Now days we have to have several hundred dollars worth of tools to do what they did for free.
Aren't most dual fours progressive? Opening both at the same time is a good way to spell bog with a common plenum.
Quite a few factory dual fours used solid linkage. How well it runs depends on the selection of carburetors, and the ability of the tuner. Jon.
50 years ago, we didn't have to contend with owners that thought dual Dominators on an otherwise stock 283 ought to be a killer street engine! I played with multiple carbs for several years before I saw a uni-syn. Jon.
I used a uni-syn on mine for idle and have not adjusted them in 2yrs. I run off the rear one under normal driving and open them up at least once a month. When dead cold I must floor the throttle to squirt both to start, after that when warm I don't even touch the pedal to start. Because they are Carter WCFB's I made the adapter for the uni-Syn from parts on e-bay.
I have found that measuring the primary throttle blade openings with feeler gauges worked best for me. Just using the idle adjustment screw and counting revolutions was too innacurate. Check and verify wot on all eight butterflies.
When I started on my dual single W-1 carters, I backed the throttle stops all the way off so the butterfly was closed all the way. I then rigged up a dial indicator to the linkage and started turning the idle speed screw out till the throttle was open " x " amount. I did this on both so I knew each was at the same spot. Once it started, I could adjust the speed with the same amount of turn to each screw. I also found it worked best to unhook the linkage so each could be adjusted separately, then fiddle with linkage to get back on without changing the carburetor adjustments.
I have 3 cars in the garage with 2x4 setups, low rise, tunnel ram and blower all with one to one linkage and all run great. I also tune by vacuum gauge, dwell meter for tachometer, ear and feel. Each gets you a little closer once you figure out what you're looking for, which doesn't come overnight but is achievable.
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