Turn the canisters upside down and keep them higher than the nozzle to have liquid propane to ignite. That should look more like what people expect when they hear flame thrower. Perhaps puff and sip control. Ruben’s does it’s thing automatically. I think getting the guitar to adjust the flames as to how it’s played may be several degree more difficult. I recall a time when a band playing at the Sherman Tank in Goodland, KS thought it would be far out to light the drums on fire as the drummer played on. Not a good idea on a stage with a low combustible ceiling. They didn’t burn the place down, so I guess only royal ass chewing was all that come of it, as well as contract stipulations, that weren’t there before.
Full article: http://hackaday.com/2013/07/31/flamenco-guitar/