Quite some time ago I was given an old MightyMig 100. The feed was very erratic: the wire would not feed smoothly or it would simply stop, even though the motor was running smoothly. Constant adjustment, new liners, clean rollers, new tips and fresh wire made no difference. I then looked closely at the roller assembly and realised that the plastic from which the outer support for the feed roller was made was slowly crumbling like Edinburgh rock. The more that I adjusted the tension, the worse it crumbled, stopping the roller from exerting any pressure on the wire. I fabricated an alluminium replacement part and the machine now welds faultlessly. If anyone else has similar, elusive problems, it might be worth inspecting this part carefully. James.