I had a similar problem with my millermatic 180. I found my problem was when I moved the welder I was pulling the whip slightly out of alignment of the tube where the gas needs to be.
I pushed against the outside of the whip felt a slight nudge ahead. That fixed the problem. Like 57 blevins mentioned I was loosing gas shield. It had been acting the same as if I had been welding in the wind, but I was inside. Maybe you can check all the tubing connections to make sure the gas is getting to the source. Good luck, hope this will help.
