Ported Vacuum Control System

As throttle blade opens, a slot type port in the carburetor throttle body is exposed to an increasing percentage of manifold vacuum. This port is connected through the Coolant Control EGR Valve to the EGR valve. Flow rate is dependent upon temperature, manifold vacuum, throttle position, and exhaust gas back pressure. Wide open throttle EGR operation is precluded by calibrating valve opening point above manifold vacuum available at full throttle.