Pulse-Air System
When the engine is running, air is drawn from air cleaner to exhaust valves via the air injection passages. The check valve draws fresh air from the clean side of the air cleaner past a one-way diaphragm made of high temperature material.
Negative pressure (vacuum) pulses in the exhaust ports and manifold passages cause the diaphragm to open and allow fresh air to mix with exhaust gases. If the exhaust pressure is positive, the diaphragm closes, and no exhaust gas can flow past the valve and into the air cleaner.
The check valve is more efficient at idle and slow engine RPM when the negative pulses are maximum. At higher engine speeds the check valve remains closed.
The exhaust gas/fresh air mixture flows through the exhaust pipes and into the catalytic converter. The oxygen in the air combines with hot exhaust gas and this furthers the catalyst reaction in the converter.