I have a 120 volt Lincoln in my truck from work. It acts up too. In my case I use flux core due to working conditions. I was talking with someone on another forum, he noticed the flux core being a little more finicky then the mig wire. I try to keep the feed cable as straight as possible which helps a lot. I've also noticed the drive tension has to be close to ideal. I found making it tighter causes issues. Just having enough tension to drive the wire seems to work the best.

There's really nothing wrong with a 120 volt welder it's just more sensitive to voltage drop. For a given amount of wire resistance cutting the voltage in half doubles the amp draw which results in 4 times the voltage drop compared to running at 240 volts with half the amperage draw for the same wattage. Ideally you want no more then a 3% voltage drop. That's why everything runs at a higher voltage. Smaller and cheaper wiring.

Welder update.  It was the liner and tip.  They charged me $15.95 for the liner and installed it for free and had a extra tip they gave me.  Cant beat that!  Though the shielding gas was $50 to fill up a few weeks ago.  That's really went up in price.  Ill give it a try tonight to make sure it working ok.   Though we dropped my son off to college last Saturday it probably wont get much work unless he comes home on the weekend to work on his Mustang. 

Australian national law on the rentals I assume?

I own all my bottle because with the limited use they get renting would be absurdly expensive.  One of the many things it seems that makes building cars in other countries more difficult than in the US.  My hat's off to you guys who do it anyway!