As odd as it sounds, I'm replacing the compressor in a window shaker. Find out that mapp gas isn't hot enough to flow silvabraze with 1% silver. Ah, well. Cheap stuff. Finally after carbonizing the heck out of the tubing. I got out my acetylene torch with the air turbo tip. That did the job. Made the copper glow, and the stick braze flow.
Someday I'll have to buy another pack of the 15% silver stuff. That flowed a lot better with mapp. The Johnstone catalog says it's the same melting point, but that's not my experience.