As stated above, the Uni-Syn carb is an excellent way to balance the carbs (I used them on VWS, Porches, and British sports cars back in the 60s & 70's). You might need to make an adapter tube to make a good seal to the top of the carbs, depending on what carbs you use. I have used short pieces of plastic pipe with a rubber gasket on the carb side of the pipe. The Uni-Syn has a rubber seal on the bottom and should seal on the top of the plastic pipe. If you make two pipes, you can easily move the Uni-Syn from pipe to pipe (carb to carb).
If you want an adequate, back-yard adjustment, it is also possible to balance the carbs with a vacuum gauge (with or without a tachometer).
1. Set the idle speed you want by adjusting one of carbs until you observe (on a tach, or, by ear) an increase (or decrease) in rpm. You can raise or lower the idle speed by going back and forth between carbs and increasing or decreasing each carb until you "balance" at the speed you want).
2. Adjust each carb's mixture to maximum vacuum after adjusting the idle speed to match on both carbs (if you have access to the mixture adjustment). This works fine with one and two-barrel carbs on the the old sixes.
3. If the idle speed is too high or two low after adjusting the mixture, go back to step one.
I've done this with stock Rochesters and with two-barrel Carter-Webers and it closely matches the Uni-Syn setting.
