mjb920 wrote:
Slightly off-topic, and maybe stupid, but is it possible to overheat
the copper pipe itself with either propane or MAPP? It seems to
discolor with prolonged heating.

The discoloration is harmless oxidation. The colors result
not from actual color change to the metal, but from light
being bent within the thickness of the oxide layer.

To avoid burning metal when soldering, speed is of the essence.
Use the hottest flame practicable -- here, meaning your trusty MAPP
torch -- on CLEAN metal. I've used these to silver solder (jeweler's
50/50
silver/copper) bottle bosses onto heavy gauge Schwinn-quality steel
bike frames. Takes about a minute to heat the joint glowing red hot,
hot enough to make the silver flow.