New 250EX owner, a few problems

[Rugar]

Try setting the preflow, postflow, upslope, and downslope all to 0, and the start amps and end amps to 100% as a test to see if it stops and starts the arc when you release the pedal or switch.

If that all works, then go to this link for a series of videos on what each of those functions does.
http://www.everlastgenerators.com/video-library.php