Oh so many things appear different in the welds. The first pass on the left in the first photo looks like you were too hot but the others look like maybe you turned it down too cold. Get rid of the paint and rust, even a professional welder cant make a pretty weld over paint and rust. Grind all surfaces at least 1/2" back from the weld area to clean, bright, grease free metal. Some areas of the weld look like you were also holding your arc too short,just dragging the rod. While some rods will weld this way, hardly any will to it over thick powder coated paint. It looks like you were using a 70xx rod, if so, a 1/16-3/32" arc would be preferable. Set your machine to where it starts welding without excessively sticking but not so high that it undercuts the base metal. Undercut is caused by either running too hot or travelling too fast. Adjust your travel speed according to the amps used.
Finally, get yourself some all cotton shirts. Even if you are using a welding jacket or leather sleeves, it is best to use cotton clothing underneath. They dont melt and are harder to catch fire than polyester or polyester blends.