Air induction
This system burns the unburned exhaust gases by injecting fresh air (secondary air) at the exhaust port. This is to reduce the output of the hydrocarbons.
When there is negative pressure around the exhaust port, the reed valve opens and the secondary air flows into the exhaust port.
The required temperature for burning the unburned exhaust gases is approximately 600° to 700°C.
Air cut-off valve
The air cut-off valve is operated by intake gas pressure through the diaphragm. Normally, this valve is opened in order to allow fresh air to flow into the exhaust port.
When the throttle is rapidly closed, negative pressure is generated and the valve closes in order to prevent after-burning.
VIEW 1. (NO FLOW)
When decelerating (the throttle closes), the valve will close.
VIEW 2. (FLOW)
During normal operation the valve is open.
![](https://motoinstruction.ru/img/yamaha/16/122438.jpg)
[A] From the air filter; [B] To the cylinder heads; [C] To the carburetor joint; (1) Reed valve