A closed type crankcase ventilation system is used to prevent engine blow-by gases from escaping into the atmosphere.
A small fixed orifice, located in the intake manifold, is connected to the rear section of the rocker arm cover by a hose. Some later models have replaced the orifice with a PCV valve. The PCV valve is generally located in the hose from the rocker cover.
A larger hose is connected from the front of the rocker arm cover to the air cleaner assembly. Under light to medium carburetor throttle opening, the blow-by gases are drawn through the fixed orifice. Under heavy acceleration, both the fixed orifice and the large hose route the gases into the engine.
The only maintenance required is to regularly check the breather hose condition, clean the orifice in the intake manifold, and clean the steel wool filter, in the air cleaner. Replace the PCV valve (if equipped) when it becomes clogged.
To check for a clogged PCV valve; with the engine running, remove the valve from its mounting. A hissing sound should be heard and vacuum should be felt from the inlet (bottom) side of the valve. Turn off the engine, shake the valve. A clicking sound should come from the valve when it is shaken. If the valve fails either of these tests, replace it.
REMOVAL & INSTALLATION
Remove the valve from its mounting. Disconnect the hose(s) from the valve. Install a new valve into the hose(s) and push the valve into the mounting.