Just to clarify.. your CO fine adjustment is the air/fuel mixture screw. Adjusting this is the "Meat and potatoes" of carb tuning. It can be done in while an emissions tester is reading HC/CO, but that's a bit of a "Lab tune" for passing the tests for JCI inspections. Here's how to do it.. -Pull the adjusting screw all the way out to inspect. It should have a smooth taper, and be clean. Sometimes, it will need replacing due to super mechanics torquing it down too tight. -Re-insert, and GENTLY snug it down until it bottoms out. -Using the flat tip slot as a guide, turn the screw CCW 2 complete turns. Turn the vehicle on, and let it warm up. -Once it is warmed up, turn the screw CCW in very small increments.. say 1/8 of a turn -The idle will slightly raise with each turn of the screw -You will get the the point where the idle no longer raises.. turn it CW until you hit the point where it first stopped raising the RPM's. You want it right on that crest. If you have a spare vacuum gauge, it will do the same job. Adjust until you see max vacuum on the needle.. but no further. Any more will just introduce too much fuel. Of course the adjustment screw is independent of any of the other physical adjustment screws.. just thought it would help to clarify.