If you are going to run a 110v feeder off of an extention cord use no smaller than a 10guage cord. If yuo get a 10 then you will not notice any difference in it's welding capabilities.
FASTBACK340
Pass on this one and as others have said, pick up a Lincoln, Miller or Hobart. I have been repairing welders for 18 years now and can tell you this one will cause you more frustration than it is worth.