So very stuck...

The carburetor does not “control” how much vacuum there is. Vacuum is generated by the engine running and the carburetor restricting the airflow. At different throttle positions and different load situations you’ll have different levels of vacuum. That’s why I said tape a vacuum gauge to your windshield, it will help you understand what’s happening and when. Vacuum is not rpm dependent, you can be at 6000 rpm wot and have zero vacuum, or 6000 closed throttle and peg the gauge. Vacuum is load dependent.