You might be able to reset the idle mixture to get into compliance at idle, it's best to do so while it's connected to the emissions analyzer so you can see the results. If it can't, suspect the cat-converter/s if all else checks out OK. 1% to 1.5% CO is pretty normal if the cat converter/s are hollow.

Make sure that the choke is opening fully when the engine is hot.

Make sure that the upper exhaust manifold is not cracked, the O2 sensor will see the extra O2 from the air being drawn in and send a lean signal to the ECM which will richen the mixture.