Barry Grant's new Old School Triple-D Six Shooter system combines the vintage look with contemporary performance. Due to the progressive linkage, the engine runs off the center carburetor most of the time; all three reach wide open simultaneously.
Of all the mechanical icons there are in the performance world, few things are more impressive than multiple carburetors. Adding another carburetor to an engine was one of the earliest tricks hot rodders came up with to enhance performance and virtually every combination from two to eight has been tried, but when it comes to V-8 engines, the coolest combination is undoubtedly three twos.
While adding carburetors seems simple enough, there's actually more to it than meets the eye. One of the most common misconceptions is that when carburetors are added the jet sizes have to be reduced to keep the engine from running too rich, but that's not the case. Although the jets determine the air/fuel ratio, the amount of air passing through the venturi determines the amount of fuel that is discharged, not how many carburetors there are. Granted this is an oversimplification, but if one carburetor delivers a 14:1 air/ fuel ratio and another carburetor just like it is added to the engine, the air/fuel ratio is still 14:1, there's just a larger volume of that mixture. For maximum performance rejetting may be required with multiple carburetors, but the same holds true for single carburetor applications.
Obviously the purpose of multiple carburetors is to supply the engine with a larger quantity of air and fuel, but just because a little mixture is good, a lot isn't necessarily better in some instances. At idle and low engine speeds, one twobarrel carburetor can satisfy the needs of most V-8 engines and three are two too many. At higher a rpm, most small carburetors can't supply the volume of air and fuel required, but three of them can. So, in most cases you'll find three twobarrel combos equipped with progressive throttle linkage. At idle and low speeds (until half or two-thirds throttle depending on the linkage design/adjustment) only the center carburetor is operating. As the throttle pedal is pushed further towards the floor, the end carburetors begin to open and all three reach wideopen simultaneously.
Because carburetors only deliver fuel when air passes through the venturi(s), if the throttle blades are completely closed the carburetor is effectively shut off. And that brings us to the differences between the carburetors used in three two applications. In most cases, the end carburetors are different from the one used in the center, that's why you just can't bolt three "regular" carburetors on a manifold and expect good results. Think of three twos operating in a manner similar to a four-barrel. The center carburetor is the primary supplier of fuel at idle and low speeds, and the end carburetors are the secondaries that open when you stick your foot in it all the way.
Barry Grant's new Old School Triple-D Six Shooter system combines the vintage look with contemporary performance. Due to the progressive linkage, the engine runs off the center carburetor most of the time; all three reach wide open simultaneously. | 
This is the center Six Shooter carburetor; it has an electric choke and idle-mixture screws. Note the two vacuum ports below the choke; one is ported, the other full time. | 
All Six Shooter carburetors have a four-bolt mounting pattern. The end carburetors are not equipped with a choke valve or idle-mixture screws. |
Barry Grant has simplified float adjustments with a sight glass on the right side of the float bowl (arrow). The float adjustment is the screw and nut on the top of the bowl. | | |