Also use a nozzle with say a 5/8" dia. orifice as this will give you better gas coverage. A small orifice will cause trouble when a little spatter build up happens. This will cause turblence in the flow of gas. Small orifice nozzles have their places and that is in narrow and hard to get to places. Check the machine for the proper CFH. I have always used 20 to 25. A lot of people think that, hey the weld is not looking good so I will turn up the CFH up all the way. This to will cause turblance and that turns into porosity. If you are using a guage with a ball then the top of the ball should be at the line of the CFH you want. Wipe the material to be welded with a cleaner, ( not an oil base cleaner, leaves an oily film). These things will help in producing a quality weld. Remember clean is always better for welding. Sometimes it is not possible but when it is. Do it.