I'm going through this myself. CO was high at 2500 rpm, but was 0% at idle.
Was your CO high at idle, at high rpm, or both? High CO can be an indication of running rich. If it was just high at idle, it could be the idle mixture. This is an easy fix. If it was at high RPM, your carb might need some TLC. I rebuilt mine since it needed it anyways.
Another possibility is the air injection system. This isn't too difficult to diagnose yourself if you have the emissions manual. A bad smog pump could cause CO to be high. Check all your hoses thoroughly though; I discovered that the hose going from my ABV to the air injection rail was almost completely destroyed at the check valve. My pump seems to be putting out a decent amount of air, so I suspect the busted hose was the main problem.
A bad catalyst could also cause high CO, but I'd think that other pollutants might be high also if it was bad. In my case, I'm going to ignore that possibility until I've had a retest once I get my air injection parts installed.
There are probably some other tune-up related things that you could recheck too, like valve adjustment, timing, functioning advance diaphagm, etc. I don't know how much those affect CO specifically, though.
