Vacuum Controlled Progressive Linkage

Progressive linkage makes use of a vacuum diaphragm unit. Its purpose is to insure that second barrel of carburetor comes into action at proper time to satisfy engine requirements and air pollution control requirements. Vacuum, which actuates diaphragm, is taken from Venturi of the two barrels. In Venturis, vacuum decreases when throttle plates are opened, and vacuum increases as RPM increases. Action of diaphragm is progressive and provides a smooth transition from first to second barrel.