Re Williams Oil O Matic
They, like GEs oil burner,were low pressure burners,these used a adjustable nozzle that rarely ever needed any attention,and could burn less expensive heavier oils cleanly and efficiently...they were more expensive to build than the standard high pressure oil burners,this and the fact most service men did not bother to learn how to correctly work on them,led to their demise, as well as the Wall Flame Rotary burners which also were very clean burning trouble free units,many of these units were giving 80 plus efficiency ratings in the 50s when the standard oil burner units were giving 60 to 75 percent efficiency...especially the GE units, they were complicated in that their control system was totally different than any other furnace,safer and better built also, but were way ahead of their time.