Al, I don't believe that what I am seeing is mostly vapor (although there is possibly some).  If your theory is correct then lowering the pressure at the regulator would decrease the pressure drop and less vapor would be made and the return flow would decrease.  This is opposite what I have found.

Dave;

I didn’t mean to infer “mostly” vapor just “some” bubbles.  I recall a conversation with someone (maybe Greg at GRT) and was told bubbles, or pulsations from the pump if located just downstream, will cause high readings.  You’re right about the effects of regulator pressure; so I don’t know.  It could also be your pumps pump more and that the readings are correct.  I know Tracy has sold different pumps at different times.

Also, even if it is mostly bubbles (foam), there is still 40-80 gal/hr of something going through that return line so it should be big enough to handle it.

From what I’ve heard, there are likely “some” bubbles.  I am aware of a case where the bubbles were observed in a clear walled tube used for the return line.  One guy with a Subie on a Velocity had trouble with foam coming out of the vent line from the sump tank.  I think he added a section of large diameter tube where it could condense.  I’m hoping not to see that, and will keep pump #2 in backup status.  My circuit diagram still shows pump 2 switched on by a pressure switch which closes on low fuel pressure, but I’m have trouble finding the pressure switch for gasoline.  They are specified for oil, or for coolant. 

Al