[ohecht]

The small set screw inside the WUR changes the sensitivity of the second (smaller) bimetal strip in opening the set of contacts visible in the photo I posted. At the plug connection on the outside of the WUR, I get 25 ohms with these internal contacts closed and 10 ohms with them open. It seems that this is the way the WUR regulates the warm control pressure, sort of like a simple thermostat to reduce the amount of resistance through the larger bimetal strip as everything warms up.
Actually, now that I think about it again, it is probably to alter the speed that the WUR moves the system from cold to warm control pressure. The small bimetal strip is not heated, so it is only affected by the ambient temperature inside of the WUR, which would be mostly dependent on the outside air and engine temperature. A closed internal contact during warmer conditions would heat the larger bimetal strip more quickly, so the car would not run rich for as long. In colder conditions, the large bimetal strip will get less resistance and the car will take longer to go from the enriched to the lean state for warm running.

Olivier