Since the gas tank was swapped at some point and I suspect is a newer MK2 tank I am not certain that the BSA EWARTS fuel valve is original. The higher resolution FOIA picture that I now have does look correct except it is on the left side not the right side. Complicating matters further is that the valve came apart about a month ago and I lost the plunger, retaining screw, most of a tank of gasoline and my son’s fancy leather boots. Below is the best picture that I could find of the original unit. I suspect I could find the plunger with a metal detector since I know roughly where it fell out.
A new BSA cork lined plunger was easy to find. The retaining screw was not. I finally found the correct 6-40 threaded screw in a gun shop. The retaining screw is too long but I have equipment that can make stuff shorter. Hopefully cork is rated for Ethanol. The new plunger is plated. Not sure if it is chrome or Cadmium.
The fuel outlet threads are 7/16-19. This might be an obsolete JIS -3 thread. The tank threads appear to be G1/8-BSPP which is another obsolete Whitworth thread. There was a Phenolic fiber washer between the tank and valve.
Edit: The phenolic washers showed up and are a perfect fit. They are .062″ thick which is about .020″ thicker than the original washer but that is what worked on the right side of the tank. Since I want to match the SFII picture that shows the valve on the left side I will have to sand the washer to get the valve to clock correctly on the tank. The G1/8-BSPP straight threads will not correctly accept 1/8-27 NPT tapered plugs without chasing the threads with a pipe tap on the right side. I still need to shorten the retaining bolt.