Little Torch won't keep a flame with only propane.

Hey everyone I am looking for advice and I don't know if this is the place. I've gotten into copper and silversmithing recently and have been having a lot of fun and even made a few pieces successfully. I got a knockoff Little Torch that is not supposed to be as good as a Smith's, but is supposed to function. When I ignite my torch with only propane (no oxygen going through it) my torch ignites but it won't keep a flame with only propane. I've tried with both valves open and my flame will just dwindle and die very quickly (matter of seconds). Does the torch need to have the oxygen running also to keep going? I've used propane before so this is weird behavior to me. Sorry if this isn't an appropriate sub to get advice from.