Sounds like a bad liner!! It could also be the wrong size tip. If it is burning back into the tip, the wire isn't feeding fast enough for the heat range. If the tip is too large, the voltage spikes because it is arcing from the tip to the wire.
Check the wire feed with the gas off and the heat turned all the way down. You're not trying to weld. If the wire feeds jerky or you hear or feel it dragging in the liner, you need a new liner. Remove the tip from the stinger and slide it onto your wire. It should slide freely and still fit tightly on the wire.
Once you get the feed problem worked out, you'll throw rocks at that Hobart!! A TweeCo hose and gun are my choice to go with this, or any unit!! I'm currently using an ancient Linde that I've had a bunch of work done on, including a new TweeCo gun. I've 'bout got it trained to do what I want!!