What's this on the carburetor of motorcycle? The wire rope is empty and not installed. It looks like a throttle valve. There was no response when it started and turned back.

The picture is not very clear. Looks like an accelerator pump. This acceleration pump only works when it accelerates rapidly, but it doesn't work when it turns the throttle slowly. Its function is to spray more oil from a nozzle in the throat of the carburetor during rapid acceleration, so as to improve the instantaneous acceleration ability. If you remove the intake pipe of the carburetor on the air filter side and tighten the throttle quickly, you can see that the small pipe will spray more oil.