Well, I decided to not wait until it gets cold out and try and do some matinence on my natural gas furnace while the weather is warm.
I cleaned out the fire box, and cleaned the gas jet, replaced the thermocouple and re-assembled everything.
The pilot light stays lit, and everything seemed fine until I turned up the thermostat. The firebox lit up, but not before a large back-flash shot out behind the gas unit. After the flash died, the furnace was running fine.
Needless to say, I don't want fire shooting out the back every time the furnace kicks in.
So far, nothing is adjusted for flame color and venting. Will this go away after the air mixture is correct, or am I missing something ?
Jim