If an engine idles roughly, check for a clogged crankcase ventilation valve, or a clogged air cleaner element, or a plugged hose. Replace the valve, the element, or the hose as required. Use the following procedure:

1. Remove the crankcase ventilation valve from the rocker arm cover.
2. Run the engine at idle.
3. Place your thumb over the end of valve in order to check for a vacuum. If there is no vacuum at the valve, check for plugged hoses, the manifold port at the TBI unit, or the crankcase ventilation valve. Replace the plugged or deteriorated hoses or the plugged crankcase ventilation valve.
4. Turn OFF the engine. Remove the crankcase ventilation valve. Shake valve. Listen for the rattle of a check needle inside the valve. If the valve does not rattle, replace the valve.

This system exhausts any blowby in excess of the system capacity (from a badly-worn engine, sustained heavy load, etc.) into the air cleaner. The system draws the blowby into the engine.

The proper operation of the crankcase ventilation system depends upon a sealed engine. If you observe oil sludging or dilution and the crankcase ventilation system functions properly, check the engine for a possible cause. Correct the problem in order to ensure that the system will function as intended.