While it never got much respect from the high-performance community, the Rochester Quadrajet carburetor did an admirable job on millions of General Motors vehicles through the years.

Sure, we’ve heard all the jokes and nasty nicknames, including “Rottenchester Quadrajunk.” Nope, the hot rodding community never fully warmed up to the Rochester Quadrajet, the ubiquitous GM four-barrel carburetor that was produced from 1965 to 1990. And to be honest, the carb had some significant limitations for all-out racing use, including a small float bowl capacity and lack of adjustability. But in the role the device was designed and engineered for—everyday road use on all sorts of production gasoline engines from 230 to 455 cubic inches—the Quadrajet performed its job admirably for four decades.

Formally unveiled in 1965 on Chevrolet’s new 396 cubic-inch Mark IV V8, the Quadrajet boasted one instantly recognizable feature: The primary and secondary throttle bores were of radically different diameters. The tiny primary apertures provided precise idle control and crisp low-speed throttle response, while the gigantic, air-valve operated secondary bores provided the high-speed fuel and air delivery. The totally sensible setup soon earned a name, “spread bore,” as competitors Holley and Carter developed their own adaptations of the configuration.

The Rochester Products Division was originally founded in 1916 as the Rochester Coil Company and was acquired by GM in 1929. In 1953 the division expanded from electrical components to its first in-house designed carburetor, the 4GC. While no official figure is available, it’s been estimated that Rochester carburetors have been used on more than 150 million GM vehicles.

The illustrations above provide the two most important pieces of information required to service the Quadrajet: first, the location of the carburetor ID number, needed to obtain specifications and parts, including rebuild kits, and second, the procedure for adjusting the float level, which is far and away the most important setting on a Q-jet. In truth, there aren’t a lot of adjustments or tunable components on the carb, which in the hot rod world is both a blessing and a curse. Another nice feature of the Quadrajet is its simplified, one-piece float bowl and body casting, which makes it far less prone to fuel leakage than some other carburetors.

Countless varieties of the carburetor were produced over the years: with and without integral choke units, straight and 90-degree fuel inlets, and so on, and in 1980 an electronic version was introduced with a solenoid-operated primary circuit to provide closed-loop air-fuel mixture control. Some Quadrajets were manufactured for GM by Carter (they are virtually identical to the Rochester version) and believe it or not, the carb was also factory equipment on some Ford and Chrysler vehicles.

After the Quadrajet was discontinued by GM, speed equipment maker Edelbrock continued to offer a version of the carb (manufactured by Weber USA) to the performance aftermarket well into the 21st century. While the carb works great for road use in all sorts of applications, in this day and age it can’t really compete with electronic fuel injection. The spiritual successor to the Quadrajet, if you will, is the Holley Sniper EFI Quadrajet system (below), ensuring that the Quadrajet’s basic spread-bore concept will be around for years to come.