I have tripple Mikuni's with an inline Holley fuel pressure regulator. It has a tap for a fuel pressure guage that I recently got around to installing. These carbs prefer approx. 3-1/2 psi. My guage was showing 2 psi. I opened the regulator up further and further and still could get only 2psi max.

Well the fuel pump is 15 years old but in terms of mileage it has maybe 20K miles on it at the most. I decided to replace it with a new one thinking that could be the problem.

After I am done replacing, I start car and see what I have now for psi. Its still reading 2 psi!

It finally just struck me sitting here that I have the fuel return line hooked up.

That has to be it. I am wondering now if the SU's had a restricter in the return. I sold my SU set up a long time ago so I cannot look. What do you guys think?

Yes there is a restricter in the return line. right at the end of the rail where it attaches to the rubber line at the front of the valve cover . the end of the rail was closed with about a .015'' hole in it . Try a pump from a RX-7 , one from a carbed engine , not injected . I bought mine for $15.00 at the bone yard 3 yrs ago and it works great. We tried it on a tripple Mikuni's setup on stroker engine and it worked vary well . Gary