I have got into a few arguments with the people whom are spray/ Nozzle burner disciples. Your experience is repeated many times. I can't for the life of me understand why people pay so much for these things then have loads of trouble with them and unlike yourself, stick with them and champion them as the best solution for oil burning? I would want the things to switch on and off like a lightbulb for the cost, complexity and amount of support gear the things need.
I recently Dug out an old burner from about 5+ years ago from my mates shed. It's dead simple and cheap to build and works great.
You can see a vid of it here.
As can be seen it's just made from standard compression fittings and a 1/4 T piece. I have shot a detailed vid of how the thing is put together which will come out in a couple of days. The thing lights almost instantly with no preheating or buggering around on straight veg oil and is very controllable and stable.
I have no problems melting ally in oil drums, I did the mini melter here
in a 60L drum and another one here,
in a full size drum. These were with a drip burner as I can still get a lot more heat out of those than with anything else and more than I could need for practical purposes.
A .75 gph nozzle is less than 30 Kw. I have seen more powerful Cigarette lighters! I can push 200Kw out of my drip burners without thinking. Haven't measured the Spray burner yet but from guesstimation, I don't see 100Kw+n being a problem.