Air Injection System - CARBURETED Models: Operation
The belt-driven air pump supplies air under pressure through the one-way check valve through an air manifold to the exhaust ports just above the exhaust valves. The air combines with exhaust gases to continue the oxidation process in the exhaust system. The check valve prevents reverse flow in the air injection manifold when exhaust gas pressure exceeds air pump pressure. A pressure relief valve, built into the pump, controls maximum pump output. The pressure relief/diverter valve also dumps air when the engine decelerates, to reduce backfiring.
The gulp valve provides a quantity of air to the intake manifold under high manifold vacuum, such as sudden throttle closure. This additional air compensates for a temporary over-rich mixture caused by evaporation of the residual fuel on the intake manifold walls to form a leaner mixture that will burn in the cylinders.