The article on making the WUR adjustable is by Jay Pineau, Ark-La-Tex Region, PCA, in Volume VII, pages 116-117 of Up-Fixin. In case you don't have that, here is the text:
An engine equipped with a Bosch CIS (K-Jetronic) fuel injection system depends on the accuracy of the control pressure for starting and driveability performance. If during a system pressure and performance test it is determined that the warm-up regulator is at fault, you are faced with an alternative: replace it (list price now about $280) or attempt to repair it.
The regulator is a fairly simple device which varies the control pressure with temperature (both engine and self-induced via an internal heating element). There are two main causes of malfunction: heating element failure and foreign material in the metering chamber.
A quick check with an ohm meter will determine if the heating element is defective. It should read 18 to 22 ohms resistance (I didn't get this exact reading, but it wasn't an open circuit). If the element is faulty, the regulator must be replaced unless you can locate a replacement heating element from a used regulator.
If satisfactory, the regulator can be carefully disassembled and cleaned. Take care that the two small orifices are completely clear. If the diaphragm shows any wear, flip it over at reassembly. (Be careful here-the diaphragm is VERY thin metal. I didn't disassemble the bi-metal spring, just pushed it aside to remove the diaphragm.)
After re-installation, it may (WILL) require readjustment to obtain correct pressure relationships. (These pressures vary with the year of the car and the part number of the WUR. You can find them in the shop manual. If you don't have them, I can Xerox and snail-mail)
Bruce Anderson described in PANORAMA (October 1984) how this adjustment can be accomplished by "knocking the plug". The only problem with this procedure is if you "knock" it in too far, you must remove and reassemble the regulator to "knock" it back (indeed true, I tried this method). By the time you have obtained the best cold and hot values, you may have to do it several times.
The unit can be modified to provide for external adjustments by the addition of a pull-out screw and nut which permits very accurate movement of the plug."
The article also includes a diagram, but essentially you drill and tap a 5mm hole about 10mm deep into the center of the plug. Then drill a second 1.5mm hole in the crack between the plug and the WUR body. Put a 1.5mm roll pin in this hole and tap it down flush with the body (the idea is to keep the plug from rotating when you move it up and down with the pull-out screw).
Put a 5mm allen-head screw, with a washer slightly larger than the plug, and a 8mm diameter nut, into the 5mm hole. Keep the nut backed off, and gently tighten the screw until it bottoms in the hole. Now, to raise the plug (higher control pressure), hold the screw with an allen key and tighten the nut (it's a tight fit, but an 8mm box-end wrench should fit over the head of the screw). To lower the plug (lower control pressure), hold the screw, back the nut off, and then tap the screw (I use a brass drift and it takes a fairly hard whack).
Of course, while you are doing any adjustments, you need to be looking at the control pressure. I bought a CIS gauge from J.C. Whitney for less than $60. Be sure that the electrical connector to the WUR is disconnected when setting cold control pressure, and that the engine is dead cold. To get the fuel pump to run, jump terminals 30 and 87a on the fuel pump relay socket (on my 83, it is the red relay in the luggage compartment).
If your car doesn't have an O2 sensor, you are completely dependent on correct fuel pressures and mixture setting to get the engine to run correctly, so the WUR is important. After I did the WUR modification, I am confident that I can set my engine up properly, and it starts and runs perfectly, cold or hot.