The oil needle of the scooter goes up and down. What happened?

If the carburetor you use is a vacuum diaphragm carburetor, it is normal that the throttle valve (the oil needle installed inside) floats up and down with the change of engine speed.

Because the throttle of the vacuum diaphragm carburetor is automatically adjusted by the force of its diaphragm on the airflow, when the butterfly valve of the carburetor is closed, the throttle will drop to the lowest point by its own weight to maintain idle speed.

On the contrary, when the butterfly valve controls its opening through the throttle pipe, the throttle valve will drive the oil needle to rise with the change of air flow.