WALBRO Pump for Carbureted System??

My problem is when it's cold it will read say 8lbs. After it warms up
Tbe PSI will drop off a lot. Like in the 4 psi range. I'm starting to think
I might have a bad regulator. After adding a restrictor in the return line I
thought I had it taken care if but it's not. I will
Swap out the gauge and see if that helps. I will do one change at a time
Until I find tbe problem.