I have an old coal gravity furnace that's been converted to natural gas. I'm having trouble with the pilot kinda. The pilot works and stays lit. The problem is, its building up carbon deposits on the burner plate above it. I remove the carbon and its back after a single heat cycle. What this does is the buildup blocks the pilot from heating the thermal coupling that creates the .750v to open the burner valve. There is a breather tube next to the pilot/thermal coupling bracket. I'm pretty sure its not aligned correctly, causing the carbon buildup from lack of oxygen. Do you have any idea what the correct alignment is? Or could this be another issue? After it cools down, I can take pics, if it will help.