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.