Thanks for your replies.
The motor runs fine and responds to the speed control.
The donor told me that it does spark OK - just didn't feed. Will confirm as suggested before spending money.
Previous user also managed to break the plastic mount (which is repairable) for the roller tension...
Long story short:
Colleague: "Want a welder? - something wrong with the feed. Cluttering up the shed. I'll never use it. Otherwise its going to the tip."
Me: "OK" - nothing ventured, etc.
Result - Get it home, 2 minutes with a screwdriver to discover that one of the gears in the wire feed...