Hello Chuck,
Yes, this is a valid test procedure I have used. Loosening the hold down screws will rich-en the mixture by allowing the assembly to raise. If you find out the pitch of the screw thread, then count the turns you can get an accurate dimension. Not good for a fix, since this will also alter warm running!
I would make certain that the "heat feeler" (the coolant thermostat unit in the WRD, pin moves outward as engine temp. increases) is moving to specs and the slide valve is free in it's bore. Remember, adjustments in the WRD will change mixture at all temperatures not just cold. Changes in the bottom stage (oval shims) will change the mixtrue in all speed ranges and will not alter the closing temperature of the aux. air supply to the WRD. Changes in the upper stage (adjustment nuts or round shims), also change the mixture at all temperatures but changes here will also change temperature that the auxiliary air to the WRD is shut off. The heat feeler is most important and really does all the cold temperture adjustments. It has a set demension to travel as engine coolant temp. changes. Check the heat feeler.
So it seems to me that adjustment of just the cold temperature mixture without altering the warm running mixture is very limited. The root of the problem is often inadequate fuel supply or pressure, defective heat feeler, Stuck slide valve in the WRD, previous mis-adjustments, or worn or damged IP.
Basic engine tuning items should always be checked first (ignition, timing etc.).
