I started out working with 3-carb setups on flathead F_rd V-8's on 1/4-mile round track cars, running Stromberg 97's and alcohol. No problem with idle or midrange settings, because we were either wide open or off. On a street engine, the throttle plates must be synchronized exactly, to assure that all the carbs on a single intake plenum get equal venturi velocity. Otherwise, one carb will go from idle to midrange before another, creating rich or lean spots in individual cylinders. Ditto on power valves. On the old Buick and Hudson multi-carb engines, the second carburetor acted like a 4-barrel, going from closed throttle to wide open in a very short time, and those ones had no idle or midrange system. The second carb was for wide-open operation only. The Corvair 4-carb system, and the Pontiac and Olds 3-2 setup worked the same way, with the secondary carbs being vacuum-operated at full throttle. With 2 or 3 times the parts to deal with, the possibility of problems increases exponentially. My Suzuki GS550 motorcycle has 4 carbs, one for each cylinder, and must have all the throttle plates synchronized, plus idle adjustment for each cylinder. That's an all-day job sometimes!
Jerry
