The 4G carburetor is equipped with a manually-operated choke valve. Some 4G carburetors are equipped with a vacuum controlled governor to control engine speed (RPM) on heavy-duty truck applications.
The 4GC carburetor has a fully automatic choke.
Originally Rochester identified the 4-Jet carburetors with a triangular tag mounted on the air horn. Early 4-Jet tags were brass, but was changed to aluminum during 1956/57. If no tag is present the last 4 or 5 digits MAY be stamped on the air horn.