When adjusting the carburetor idle speed on an underbone motorcycle, what is the role of the throttle stop screw compared to the pilot mixture screw?

1. The throttle stop screw physically sets the minimum height of the throttle slide, while the pilot screw adjusts the air-fuel ratio at that idle position.
2. The throttle stop screw adjusts the float height, while the pilot screw controls the main jet.
3. The throttle stop screw regulates the fuel pressure, while the pilot screw controls the air intake filter.
4. They are identical in function, with one serving as a safety backup for the other.