IIRC,the CO setting is checked at idle,around 700-800RPM
Make the adjustments in small incriments,no more than 1/4 turn at a time as a little bit goes a long way!
It would probably be a good idea to "center" the fine tuning knob on the ECU before starting any adjustment.
My car was WAAAAAY rich and we got the CO to about 0.35% by adjusting the MAP.Runs much better,better throttle response(my main complaint),and about 2-3 MPG better as well.
The CO varies by model year,you will need to check your under hood label to be sure.Mine (1974)was 1% or below.
Before getting access to the CO meter,I tried to adjust by using vacuum gauge to get highest idle vacuum.This did not work at all as highest vacuum resulted in very rich mixture!