The Rochester Dualjet was a 2 barrel carburetor used from 1975 to 1987. It was developed from the 4 barrel Qudrajet and was basically the primary (front) side of a Quadrajet. The carburetor was brought into production very quickly in response to a need for improved fuel economy resulting from gasoline shortages that started 1973. The first Dualjets (on the Oldsmobile 260 V-8 in 1975) used a Quadrajet 4MC casting with the secondary side of the airhorn blank and no secondary throttle plates or shaft. The carb bolted onto the intake using the same flange as a Quadrajet, but the intake lacked openings for the secondary throttle bores. This was the 2MC Dualjet.
Starting in 1978, there was a half-moon shaped casting which eliminated the vestigial secondary side left over from the QJet. This carburetor used its own specific flange. This was the M2MC and M2ME model, depending on whether a hot air (C) or electric (E) choke was used.
Dualjet M2ME carburetors were used on 260 Oldsmobile, 301 Pontiac and 267 and 305 Chevy V-8s until 1982, as well as 200, 229, 231 and 252 V-6 engines until 1987 in both the M2ME and E2ME (computer controlled) versions.
Early 2MC (1975-1978) carburetors had the carburetor number in the same location as Quadrajets, above the secondary throttle shaft on the driver's side. After that, the half-moon M2M and E2M Dualjets had the carburetor number stamped on the rear of the carburetor.
Rochester carburetor number locations