Can pedal 125 vacuum diaphragm carburetor stop valve be used?

The air cut-off valve you mentioned should be called choke valve and acceleration pump. Although it is a part of the carburetor auxiliary system, it is indispensable. Its main function is to prevent the mixture from thinning instantly when the throttle valve is suddenly opened.

If removed, when the throttle valve is suddenly opened or closed, the mixture will be diluted instantly. Such as rapid deceleration shooting or delayed acceleration response.