ORIGINAL: Dan767
If you're using standard solder (rosen core) it won't work. Silver solder with a liquid flux (or paste, I prefer liquid) will do the job with the Weller gun you have. I use this from Great Planes:
http://www2.towerhobbies.com/cgi-bin...&I=LXFS75&P=ML. Be sure and clean the joint after you're finished, or it will corrode.
Standard 60/40 rosin core solder will work just fine. In fact, I've tried to use silver solder before, and couldn't get it hot enough. then I got some advice from a few experienced modelers about just using regular solder. It worked like a charm, and has never failed me.