I preach to all of the oil burners on the forum about getting their furnaces hot enough. It would probably be a good thing if I took my own advice.
I just got a new supply of silicon so I fired up the Brute yesterday in the big furnace to make some Everdur.
I put some scrap Everdur in the crucible for a puddle to push the copper wire under to prevent major oxidation. I fired it up with the propane feed until the crucible was red hot and then switched to oil, but I could not melt the scraps. If I turned the oil up it would smoke and the blower was maxxed out. Finally I surrendered and turned the oil off, turned the propane back on, and really let it roar. (Propane needs a lot less air than does oil.) The scraps melted. I switched back to oil and it then it burned fine.
The first point is: you have to get your furnace good and hot before you turn on the oil if you are using a drip feed waste oil burner.
The second point is a bit more theoretical. I could be wrong here, but it appears that with an inadequate supply of air, the oil has to be really hot so it can vaporize in the furnace. It appears that less air is required to burn thoroughly vaporized oil than is required to burn partially vaporized oil, and that initially it takes more air to get the furnace going good and strong, hence the need to get the furnace really hot, as in the case here. In my small furnace the same shop vac blower is more than adequate and delivers enough air that I don't have this problem.
The third point only applies to me: I really need to build a bigger blower. My blower is a 5 gallon shop vac, and it is not quite enough for the Brute in this furnace.