I got in touch with the original owner of the burner, and he confirmed it is for propane. A closer look shows me that the nozzles are not working right, I can see gas (flames) leaking out of the bottom where they screw in. So I'm thinking they all need to be cleaned up - soaked in something (what?) to remove whatever is clogging them, make sure the threads on the burner and nozzles are clear, etc.
Any suggestions or other ideas?