Carbureted Models

Fig. 24 EGR control valve:

This system is used to reduce oxides of nitrogen emissions at the engines exhaust. This is accomplished by introducing exhaust gases into the intake manifold at throttle positions other than idle. The system uses an EGR valve. The exhaust gas intake port of the EGR valve is connected to the intake manifold exhaust crossover channels where it can pick up exhaust gases. As the throttle valves are opened and the engine accelerates, vacuum is applied to a vacuum diaphragm in the EGR valve through a connecting tube. As the diaphragm moves up, it opens the valve in the exhaust port which allows exhaust gas to be pulled into the intake manifold and enter the cylinders.
Two different type systems are used to control EGR operation. A Ported Vacuum Control System and Venturi Vacuum Control System. Both systems use the same type exhaust gas recirculation (EGR) control valve, Fig. 24, only the method of controlling the valve is different. The valve is a vacuum actuated, poppet type unit used to modulate exhaust gas flow from the exhaust gas crossover into the incoming air fuel mixture.