check the mixer (carb), it should have an screw where you can set the CO.

The trim valves are supposed to be set 50/50 (duty cycle), this way they can adjust mixture up or down, setting them to 50/50 value is done by the mixture screw. Diagnosis software is needed to set the duty cycle.
Also, you can adjust the range of mixture setting by adding thin plastic shims under the cone of the mixer.
Daewoo/Doosan had lots of issues with this in their 2-3 series, also different spring rates for the mixer and regulator where available at that timespan.