That is the pilot set screw also often called the mixture screw (first pic) as it adjusts the mixture from idle to about quarter throttle. The setting is 2 turns out from fully screwed in, lightly, otherwise you may damage the taper. 2.5 turns out will make it run rich at idle. If set wrong like 2.5 turns it can make the bike run badly below half throttle which is about 5000rpm as it has to clear the plugs of carbon from the over rich running before picking up on the main jet properly. (Might be reillypadraighs problem) On the fazers it adjusts the fuel flow in the pilot jet circuit. It has nothing to do with vacuum which is controled by the idle screw on the left side of the carburettor bank and the throttle with your right hand. The main jet and slide needle control the fuel flow from quarter to full throttle.The more you open the throttle the more vacuum created in the inlet tract.
Remove the carburettors and set it to 2 turns out which is 2 x 360 degree turns. You can adjust them in situ, but it is very difficult to confirm the accuracy unles you have CO2 meters. They are set at the factory using CO2 meters plugged into where the bolts are on the downpipes. Which is why they may not be exactly 2 turns but very close to 2 turns. When setting up the fazer carburettors 2 turns is the start point.
Remove the carburettors and set it to 2 turns out which is 2 x 360 degree turns. You can adjust them in situ, but it is very difficult to confirm the accuracy unles you have CO2 meters. They are set at the factory using CO2 meters plugged into where the bolts are on the downpipes. Which is why they may not be exactly 2 turns but very close to 2 turns. When setting up the fazer carburettors 2 turns is the start point.