To solve this problem, the positive crankcase ventilation (PCV) system circulates fresh air through the crankcase in order to pick up blow-by gases, which are then rerouted back to the engine through a carburetor. Vacuum hoses and a PCV valve, which regulate the flow of gases according to engine speed and manifold vacuum, are the main components of this system. Carbon and gunk that accumulate in the PCV valve and hoses over time may cause them to jam, hence regular scrutiny is needed to ensure they function properly. Poor idling or reduced idle speed may indicate a restricted or stopped flow in the system. To test for proper vacuum pull off the top plate of the air cleaner and remove the hose leading to the small PCV filter. While your engine is idling put your thumb slightly on towards the end of this hose. A feeling as if there is a slight pull or suction tells that air is being drawn through it. If any vacuum is felt there should be further checks since low or no vacuum will mean that blocking has taken place within this system. By shaking it you can check whether the PCV valve clicks; if it does not, it should be replaced because its check needle does not work properly anymore. When running at idle speed with valve removed, engine should result in a relatively strong vacuum pressure. If there's no or very little difference felt in terms of vacuum pressure either way it might indicate blocked vacuum hose or inlet fitting at engine manifold. Clearing out passages clogged at manifold or carburetor require thorough cleaning, while failure of pcv valve necessitates replacement thereof. When buying a new one for your engine just make sure that you don't get something else instead of genuine PCV valves.
