How well different manifolds/carbs work often depends on the port design of the cylinder head, and how the manifold ports work in conjunction with the cylinder head.
Multiple carburetors that run in "parallel" operation (all carbs operating all of the time) MUST be balanced.
Multiple carburetors that run in "series" operation (one has a "primary" carb, and one or more "secondary" carbs) require less balance.
Examples of "parallel" set-ups would be either the Corvette 6 cylinder with 3 Carter 1 barrels; or the Hudson Twin H with 2 Carter 1 barrels.
Examples of "series" set-ups would be Chevrolet 348 tripower, or Chevrolet 409 dual quads.
Contrary to popular belief, multiple carburetors are NOT difficult to balance or synchronize. I was doing these things as a 16 year-old with a piece of vacuum hose (quite well, I might add) long before I could afford the simple vacuum synchronizing tool called a "Uni-Syn" (available at most motorcycle shops). One simply must understand how to do the synchronization, and pay a little attention to detail.
Again, the big criteria on which would work the best is dependant on head and manifold design.
Obviously, one should use slightly smaller carburetors on a 3-carb set-up than a 2-carb set-up, all other things being equal.
As to the 4-barrel comment; a properly selected and tuned four-barrel might do slightly better (3~5 percent) on fuel economy than a properly selected and tuned 2 or 3 carb set-up. However the 2-carb set-up should do slightly better on power than the 4 barrel, and the 3-carb set-up (depending on head and manifold design) should do a few percent better on power than the 2-carb set-up.
As always, selection is key. Just as one would not normally place a Holley 1150 Dominator on a 235; one must also select 1 barrel carbs of the proper type, size, AND engine fuel curve for the system to work properly. Simply purchasing 2 or 3 carburetor that bolt onto one's manifold is a poor guarantee of success.
Jon.
