I used a Sears welder (made by Twecko) for years. I restored a ton of cars with it and built a few streetrods (A LOT OF FABRICATION). Make sure all your metal is clean and your grounding clamp is on clean metal too. As said before, start your weld pool on the thicker metal and draw it to the thinner metal. Think of the car you took apart and try to replicate the spot welds on the car you are building, these cars weren't designed to be welded with a solid bead. I use this technique everyday in my job as a collision repair tech.
