I just got a MM250 at an auction and plugged it up this weekend. Feeds wire fine, can even weld with it but no shielding gas is making it to the nozzle. Hooked up another regulator to my tank thinking it was the regulator that came with it but still nothing. Pulled the cover off of the box and am thinking it may have something to do with the valve at the back of the box where the gas comes into the unit. I pulled the hose off that is on the barb fitting that runs over to the gun lead and pulled the trigger to see if there was any gas coming out of it there - nothing. No gas.

Anybody have any ideas?