To me it almost sounds like your over heating the joint. My soldering/brazing has all been HVAC related, but when I started out I had trouble soldering. I was overheating the joint and the solder would ball up and run out like you described. Not enough solder or dirt/oxidation would produce the same results. Also when joining dissimilar metals, a solder or braze rod high in silver content was required. Brazing rod is a better gap filler than solder. Just some food for thought.
Soldering 16.5 rebar tie wire
in Alchemy and Formulas
Posted
To me it almost sounds like your over heating the joint. My soldering/brazing has all been HVAC related, but when I started out I had trouble soldering. I was overheating the joint and the solder would ball up and run out like you described. Not enough solder or dirt/oxidation would produce the same results. Also when joining dissimilar metals, a solder or braze rod high in silver content was required. Brazing rod is a better gap filler than solder. Just some food for thought.