which model fuel reg do you have ruby ? they have 3 or 4 models for EFI, some, stock replacement, rising rate, racing hi pressure ???
I would suss you can rebuild the regulator diaphragm and spring rates, but doubt you would need that... the nissan one fails when they get older believe me...lol ,
this is what the regulator looks like inside
you could go this route
Sard fuel regulator
or this one for the 260
Nismo fuel reg