B Series Truck 2WD L4-2184cc 2.2L 2200 2-bbl (1990)
Secondary Diaphragm: Description and Operation
Secondary Opening Vacuum Diaphragm
The secondary vacuum diaphragm gets venturi ported vacuum from the body of the carburetor where it is mounted. With no vacuum applied, the
diaphragm spring holds the secondary throttle valve closed. When the primary throttle valve is opened more than about 50~, a lever begins to open the
secondary throttle valve. This lever is spring loaded, and the secondary throttle valve will not open until the ported vacuum increases sufficiently to
move the diaphragm against its spring. As the ported vacuum increases, the diaphragm moves, opening the secondary throttle valve.
