The more accurate way is to install an air/fuel ratio gauge. They range from around $75 to over $300. The old fashion what is to tune your carb Air/Fuel ratio at idle to shoot for max vacuum on the vacuum gauge and to read your spark plugs under load. One of the neat things about a carb is that they have a wide tolerance. As long as you get the idle circuit correct and the CFM rating is close to what you need, it will pull as much fuel as it needs via the ventures when under load. Hope this helps.
Here is a graph that allows you convert you CO readings to A/F ratio. The emissions stations here in Oregon will run older cars that don't require emissions tests for free. I used to take mine in and get the readings at idle and 2500 rpm and checked against the graph to see where I was tuning wise.