on my Qingqi QM50QT-6A
which is a 49cc moped...
-the carburetor is got me stomped.
-i know that the throttle controls the air-flow via butter-fly.
-but there is a vacuum diaphragm in the center of the carburetor that controls the needle/fuel flow.

-on the filter side of the carb is a port that controls the lift on the needle and diaphragm.

-however this port needs positive pressure to lift the needle but i cant see how any pressure could build up to lift the needle being that there is only negative pressure or vacuum throughout the intake system?
kinda hard to explain but i hope that paints a picture...

can someone please explain how this carb works....thanks