Tmac,
There are a couple of tricks to soldering. First, make sure all of the parts that bind to the solder are sanded clean. If there is any corrosion on the brass the solder will not stick. Next, the parts to be soldered together must be separately “tinned” first. To do this secure the part in a fixed position and brush some paste flux onto the part with an acid brush. Then use a small flame tourch and gently brush the flame back and forth over the part being careful not to overheat the part. Touch a piece of solid core (not flux core) solder to the part but do not let the flame touch the solder. When the piece comes up to the proper temperature, the solder will flow onto the part. Do the other part the same way. After both parts are tinned clamp the two parts together in their final position and gently hit them again with the flame. Since the parts have been tinned you do not need additional flux and probably will not need to use additional solder. If you do use additional solder use a piece that has been hammered thin on an anvil and add only a little bit.
david