Crankcase Ventilation: Operation

Blow-by gases and fumes are drawn into a controlled depression chamber between the cylinder and throttle plates of the carburetor. Blow-by gases and fumes are mixed with purged air from primary charcoal canister and combine with fuel inlet mixture to be drawn into combustion chamber and burned.

The diaphragm valve assembly used in 1974 models varies the metering valve opening to the intake manifold according to vacuum and pressure acting upon it. When manifold vacuum decreases or when crankcase obtains a positive pressure, diaphragm opens valve and allows crankcase vapors to be drawn into the intake manifold. During periods of high manifold vacuum, diaphragm closes valve and restricts flow of crankcase vapors into intake manifold.