Ported Vacuum Control System: Notes
A slot type port in carburetor throttle body, which is exposed to an increasing percentage of manifold vacuum as throttle valve opens, provides vacuum directly to E.G.R. valve. The flow rate is dependent on manifold vacuum, throttle position, and exhaust gas back-pressure. Recycle at wide open throttle is eliminated by calibrating valve opening point above manifold vacuum available at wide open throttle as port vacuum cannot exceed manifold vacuum.