It's quite possible that I was getting past the duty cycle of the unit, it is a pretty low end unit. I considered that as well but not having the experience I wasn't sure. I'll do the paper towel / scotchbright cleaner solution as well. The spool is inside the welder.
I will strip out the old wire for sure, don't need the hassle of trying to clear out jammed wires!
Once again, Thanks to everyone here!