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To ensure that piston blow-by gas does not escape to atmosphere, a vacuum is maintained in crankcase. This is achieved by connecting the crankcase breather housing to a chamber in the left air cleaner backplate.
The chamber has two outlets, one of which is connected to intake manifold balance pipe, and the other to inlet side of air cleaner. The chamber outlet to the intake manifold balance pipe contains a variable orifice valve that controls part throttle crankcase ventilation.
A vacuum is maintained in the crankcase at full throttle by the vacuum on the inlet side of the air cleaner.