What is the function of a motorcycle secondary air injection valve?
2 Answers
The function of a motorcycle secondary air injection valve is to introduce fresh air into the exhaust gases emitted by the engine, thereby increasing the oxygen content in the exhaust. This allows unburned HC (hydrocarbons) and CO (carbon monoxide) in the high-temperature exhaust to undergo secondary combustion and oxidation, ultimately reducing exhaust pollutants. It is a type of engine post-treatment technology. Working principle of the air injection valve: To ensure an appropriate amount of air injection under different operating conditions, a "control valve" is installed on the secondary air valve. Function of the motorcycle choke: The purpose of closing the choke is to increase the concentration of the air-fuel mixture, which facilitates engine starting.
I've been repairing motorcycles for many years, and this secondary air injection valve is like a little helper. Its main function is to inject fresh air into the exhaust pipe during cold engine starts. It helps burn off unburned fuel, reducing black smoke and harmful emissions, especially carbon monoxide and hydrocarbons, making the motorcycle more environmentally friendly. Modern emission standards like Euro 5 or China 4 mandate this component—without it, the bike might fail the annual inspection. Simply put, it works in conjunction with the catalytic converter to make engine starts smoother and reduce pollution. If it fails, the emissions warning light may come on, performance can become unstable, and fuel consumption may increase, so regular checks are necessary. I've seen many bikes emit black smoke due to a clogged valve, which is quite annoying, but keeping it clean usually prevents issues.
