To screw the bypass out will reduce pressure.

I wouldn't attemp to measure actual pressure.

The usual procedure is to get the pump just strong enough to be able to run the engine very rich if you screw the needle out a ways.

Then try to adjust the idle needle.

Then look at you mid range. If the mid range is rich, you have too much pressure.

Readjust pressure as noted in instructions and start adjustments all over again.