Originally Posted by DannoXYZ

That's correct. Height of slide corresponds to volume of air going through carbs. It's fed and lifted by vacuum-port in front of carb-venturi. If you can confirm slides lift fully by redline, vacuum-port is working correctly.

It also lifts needle and increases gap to needle-jet. This allows matching fuel-volume to mix with air-volume. However, this is dependent upon fuel actually reaching carb-venturi to mix with incoming air. Unless secret and hidden passages in carb body have been thoroughly scrubbed, ultrasonic soaked and micro soda-blasted, there cannot be confirmation that sufficient petrol is flowing into carb-venturi.

You need to do some testing to gather data:

- starting: choke OFF vs. choke ON, is there a difference?
- revving past mid-range: shimmed needle vs. un-shimmed needle, is there a difference?

Current revving issues would indicate that carb passages are not sufficiently factory-fresh clean.