I bought the 90 about a 18 months ago and have been very unhappy with it. The feed motor jerks on and off while welding, but OK if you are not drawing and arc. The motor control is powered from the output of the big transformer and the machine acts like it needs a more stable source of power.
Sears replaced the welder, and the next one did the same thing. Sears offers no direct technical person to talk to about it. Century makes the welder for Sears, and could not offer an explanation but walked me through the functionality. I am going to try to redesign the thing myself to slavage my investment.