Soot inside burners.

On a maintenance today. YORK m# YM8M100C. Pull the burners for cleaning. Looks like somebody's been using them for an ashtray. Soot is caked into all of the burner passages. The furnace is in a very small laundry room. Think maybe it's a lack of combustion air. Clean 'em up. Fire it up. The middle burner (out of 5) has a very strange looking flame on start-up. The furnace is modulating, so after the burners light, it ramps down to its lowest settings. And that's when the flame completely starts to flutter. It moved all the way into the burner, and started to ignite directly from the orifice. So, I pull the burner assembly again. Find that the middle orifice is a little deformed. I reem it out enough to match the others. Button it all up. Burners back to normal.



Do you think that the vagrant flame caused all of the sooting? It's possible that it could travel to the other orifices and eat up all of the primary air, leaving just fuel to burn. All of the HX tubes were pulling the same pressure. Chimney draft was -0.02 to -0.03. The analysis reading was leading me to believe that I had too much draft.



336.6F Stack

12.7% O2

136.8% Excess Air

4.61% CO2

29ppm CO Air Free

12ppm CO



On initial start-up, at its lowest firing rate...



169.2F Stack

17.5% O2

446.4% Excess Air

1.93% CO2

226ppm CO Air Free

37ppm CO



Am I missing anything? I'm going back to replace the orifices. I saw a service bulletin from York for that furnace model and year regarding the orifices. I want to do a Depressurization test since the laundry room might have air issues. There are two 6" round ducts for combustion air in the room. One of them is actually pulling a negative draft.