Welcome! Sorry, I don't know anything about Spartan torches, but it is possible your regulators are not set to provide a neutral or oxygenated flame. If it is anything like the torches I have used, I set my propane at 3-4 psi. 10-15 sounds way high. I use concentrators though. I have never tried to melt boro on a Hothead, but 104 should work just fine.
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Kathy
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