To clean an oil burner nozzle, remove it from the burner gun and place it into a deep metal container. Pour enough kerosene into the container to cover the nozzle, then leave it sit for over a half hour to remove debris.
Before cleaning the oil burner nozzle, check if the nozzle is worth cleaning or repairing. Oil burner nozzles are cheap and eventually need to be replaced. Large deposits or clogging of the interior of the nozzle may not be easy to clean, and it may be easier to simply replace the nozzle.
The first step in cleaning the oil burner nozzle is to turn off the furnace, as this process could be dangerous with it on. Remove the nozzle from the oil gun by hand, or use pliers gently. Place the nozzle into a metal container and pour enough kerosene into the container to cover the nozzle. Let this sit for over 30 minutes to remove debris fully from the nozzle. Blow leftover debris off the nozzle with compressed air. To complete the cleaning, remove the filter at the end of the nozzle, and check it for clogs. If the filter is clean, reattach the nozzle to the oil gun.