Hello I have a old lennox OF3 80C, the problem is it belches smoke from the inspection port in the fire box at ignition, it fills the chimney to the point where it will shut down. We put a brand new nozzle in and new in-line filter and the furnace will run now but it still belches even after up to three minutes of operation but it still runs and then sometimes it will fire right up and there is no smoke or anything and runs perfectly. Need advice!

Sounds like a intermittent ignition problem or just a weak transformer. Also look for a split/crack in the nozzle holder. These cracks will provide a fine mist that might not light off correctly.

Thanks for the information, do you happen to know the electrode gap and spacing from front end of nozzle to end of electrode?

Not exactly on that furnace or burner design. The fire box design has a bit to do with the nozzle degree of spread and that has a bit to do with the degree of setback and electrode gap. Another item to be considered is weather the unit is designed to use solid,hollow,or all purpose nozzle for the oil droplet dispersion. To be exact it would be best to find the unit information from Lennox.

There is much more to an oil burner than meets the eye and in many cases problems like yours can be caused from improper setup or service. It takes many years for a service person to really learn oil burner service and in today's world they are becoming scarce. In this area most of the equipment has been converted or changed out to gas or heat pump and the oil is still left on some commercial units that burn between 10 and 40 gallons per hour with multi head configurations.

If you had the proper tools you could check for proper oil pressure and the discharge voltage on the transformer but just checking the length of the jumper spark with a screw driver does not tell the truth about the real condition of the transformer.

Thanks again for the information, I'll try to get a hold of Lennox/ and or a service tech that will work on it...