Since there's no call for heat yet, the boiler won't run for more than 4-5 minutes from a cold shutdown ambient temperature to set-point high limit even with a 0.85gph nozzle, so it's hard to get a handle on the readings. The factory recommended starting point was air band 0, shutter at 3. I eyeballed the flame and settled on 2 on the shutter.
In the meantime, I was able to get two readings from one cold start run between minute 3 and 5:
First reading was about 12.5% CO2 at a smoke reading of 2-3 on the Bacharach scale with the air band at 0 and the shutter at 2. I moved the shutter from 2 to 2.5 to add a bit more air, and the second reading yielded 10% CO2 and zero smoke - so it looks like I overshot my target. That's with just a half number jump on the scale. I would have loved to dial it back by a 1/4 notch, but the boiler was at high limit and shut off so I couldn't do any further testing.
By eye there's no visible difference in the flame between the original starting point of 2 and the second setting of 2.5 (on a scale of 0-10), so there's no way these can be eyeballed.
Yes, I'm aware that the difference in readings might have been at least partially the result of short run time, so I'll wait until the weather turns colder and the burner is running for about 15 minutes or so.
John