Hysteresis is just part of the problem. This system fixes leakage by the piston (or ball) and also through those three threads that separate the pressure side from the return. The new valve is so small that it restricts flow even when the ball is off the seat. Loss of pressure due to hysteresis is quite small. This new valve opens at 50 psi and closes at about 10 psi do to the hysteresis effect.. I observed the hysteresis effect by running the motor and I saw when it finally closed off at about 10 psi. My idle pressure went from about 7-8 psi to about 20 psi with the change. When I closed off the bypass hole with the set screw I had any bypass oil going thru my return line and I could see it drizzling into the tank. I actually clipped my return line from the pressure side to the tank so I could see the volume of return oil.. It returned a small amount compared to either the ball or piston which meant all the oil was going through the main bush and rods...where it should be going. I think the piston system is an improvement from the ball but it just leaks down the pressure too much. When I first tested my idea I installed a manually adjustable needle valve. I could close off the bypass completely and have 20 psi at idle but at speed it made 80-100 psi which is too high, so I knew I needed relief and the pump was adequate. The only down side which I mentioned in the writeup is on cold starts my relief is too small and I have too much pressure except at idle. So when I rode the bike I warmed it up for a few minutes before taking off. Today I only have one BSA left in my shed, my B50 so no problems with oil pressure.
How this helps anyone with a low pressure A50/65.