I can only sortta help since I have a Promaster and it uses the Freestyle trigger which is different from BKO's.
My trigger has three set screws, rear limiter, switch activation, and spring tension. I'd assume those are the same on yours but probably in different places.
If the spring tension screw doesn't make a difference, first of all make sure the trigger spring is actually there. The microswitch has some spring to it and will return the trigger by itself but you'll most likely get crazy trigger bounce. Otherwise, your spring tension screw may be too far out or in. The adjustability in my trigger seems to be within a sweet spot of a couple turns.
The stuck set screw may loosen if you heat the trigger (out of the marker) with a heat gun or flame. That will break down loctite.
I don't think any ICD gun after the "cats" like CO2 at all. I wouldn't use anything except HPA with it.