Diverter Valve

Fig. 3 Diverter valve:

The diverter valve, Fig. 3, prevents backfire in the exhaust system during sudden deceleration.
When the throttle is suddenly closed at the beginning of deceleration, the air/fuel mixture becomes too rich to burn. When the mixture reaches the exhaust area and combines with the injector air, it becomes burnable, and the next firing of the engine will ignite the mixture. When the diverter valve senses this sudden increase in intake manifold vacuum, the valve opens, allowing air to pass from the air pump, through the valve and silencer, and to the atmosphere.
A pressure relief valve, integral with the diverter valve, controls system pressure by diverting excessive pump output at high engine speeds to the atmosphere through the silencer.