Air flow meter adjustment

[griffter]

I'm going to fiddle with my air flow meter as I think the car's running a bit rich, particularly in the warm up phase. And because I'm curious. I'm as confident as I can be that all sensors/loom/ignition are working fine. Stepper clean, idle screw adjusted, vacuum advance disconnected and blocked.

So does anyone know:

a) What the CO trim adjustment actually ADJUSTS (eg CO at idle only (as an 'offset' enrichment) or all through the range (ie once there is a significant air flow, as a factor enrichment)).
b) What CO value I should aim for (at idle).
c) Why my (and others) present measured voltage on the CO trim pin on the afm is as low as 0.005v when RPI (and others) say it should be 1.0-1.5v pre-cat, 1.8v for 500.
d) Who's right.

Danke...