The pressure to the tank is not truly regulated. The check valve keeps the tank pressure relatively constant. It varies with all YS engines even of the same type. It is normally about 3 to 5 psi.
The regulator doesn't care about the tank pressure as long as it has enough to drive fuel through the system.

The regulator adjustment controls how much fuel is admitted to the engine as you transition from idle to high speed. If you open the reg screw, the plunger comes off its seat earlier in the transition which makes the transition RICHER. If you close it, it gets leaner.

The regulator has no effect on the top end and little effect on the idle unless your idle speed is quite high. The regulator normally comes into play at 2300 and above.