Brown Residue - is it kinda chunky or more like a powder coating? Probably need more gas and/or larger cup to give more shielding. Moving air can disrupt the shield, stay away from fans, open windows etc. Might be using to much current also. If the piece is small enough that it gets red while welding you will need to set it on a heat sink to keep it cool, or flood it with the shield gas. Assume you are using the correct filler wire for the type stainless you are welding. Hold the torch over the weld after you cut the arc so that gas covers the weld til its cools below red heat. The weld itself should be shiny, there is always some discoloration in the vicinity or the weld.

Steve