make sure the governor is working
With the engine stopped to throttle butterfly should be wide open and close down as the engine speeds up
On a lot of the clone carbs the throttle butterfly can be hooked up so pulling can either open or close the throttle butterfly
Also make sure the governor spring is in the right holes
The governor always tries to CLOSE the throttle butterfly and it works against the governor spring which it attached to your throttle control so the engine speed is maintained as a tug-O-war between the governor & this spring
Different carbs often require different ( in your case stronger ) springs .