Control Vacuum

Control Vacuum:

The position of the venturi valve is controlled by two forces: a spring that acts to close the valve and a control vacuum that acts to open the valve. Both of these forces are present in the venturi valve diaphragm assembly.

Control vacuum is the vacuum below the venturi valve and above the throttle plates, and is routed to the venturi valve diaphragm through the upper body, main body and the diaphragm housing. The diaphragm is connected to the venturi valve.

An increase in throttle plate opening will normally increase the control vacuum. When the vacuum signal increases, the control vacuum diaphragm pulls in against the spring and opens the venturi valve and the main metering rod assembly. Since the venturi valve is not linked directly to the throttle shaft, the control vacuum to the diaphragm which has a calibrated spring, can now modulate and select the precise fuel/air ratio for all speed and load conditions except with wide open throttle (WOT). Note that the control vacuum regulator (CVR rod) is fully lifted (up), for stabilized engine operation. This is not so for the operational modes in which the cold enrichment system is on.