If the outdoor valve is not insulated, the valve will be corroded by water vapor in the air and other acidic gases. Even if the valve is arranged indoors, its surface may be dewed in winter. After dewing, sulfur dioxide in the air will combine with water to generate sulfuric acid, which will also cause corrosion to the valve. The tightly insulated valve, the thermal insulation layer and the external protective layer form a corrosion barrier to protect the valve from corrosion.

Therefore, when the motorcycle is running, the air door is open. Another question clarifies that people often say "turn over the air door", which means to let you tighten the wire drawing on the credentials. At this time, the air door in the carburetor is actually closed. When you release the wire drawing, the air door of the carburetor is turned over.