Welcome to the forum - I've found lots of help here.
I've got a '75 Targa; I'm going to point you to my CIS troubleshooting thread from a few years back because it has some relevant info (I hope) for your car:
https://forums.pelicanparts.com/porsche-911-technical-forum/780952-sorry-yet-another-cis-troubleshooting-thread.html
I have some initial questions:
#1 - What are the part numbers on your WUR and fuel distributor? (This is necessary to know so we're all looking at the right graphs.)
#2 - What CIS components are installed on your engine aside from the WUR, fuel distributor/air meter, and cold start valve? Do you have a decel valve? Do you have the throttle valve? (I'm guessing decel valve and no throttle valve - some early '75's had the throttle valve.) EGR valve?
#3 - Sorry to ask, but are you sure you did your pressure tests correctly?
The reason I ask #3 is that I don't think it's possible for CIS to operate at 0 psig control pressure. The system pressure you state is way too low. Here is another link to Tony's write-up of how to perform the CIS pressure test:
https://forums.pelicanparts.com/porsche-911-technical-forum/888103-cis-fuel-pressure-test.html
Here's a YouTube video on the pressure test:
And another video that gets a bit more in-depth into CIS troubleshooting:
As far as where to start:
- Please report back on #1 & #2 above.
- Review the pressure test instructions and verify you did the test per instructions; if not, repeat the pressure tests and report back.
- Consider contacting user boyt911sc and ask him to evaluate your WUR. Tony is a good guy and offers rebuild/exchange services for these. Keep in mind that a rebuilt WUR will not help if your system pressure really is that low.