I got a Godzilla 128-23 last Spring at a yard sale and now have it going again (thanks to the videos mentioned here on the Board) and re-shellac'd the case. It sews a beautiful seam but I sure had to blindly experiment with the stitch length and tension settings. Except for my mom's Featherweight, this is my first experience with "vintage" machines. This one was in pretty good shape and also has the knee lever but when I changed the power cord I must have not hooked everything up correctly: the motor ran like a champ but I couldn't regulate the speed of the machine or turn it off without pulling the cord from the wall! So I converted it to a hand crank machine with reproduction parts because I couldn't find the "real" parts online. You might have to adjust the little tension screw on the end of the shuttle case -- I had to do that. Also, would any of the shuttles from your other machines work in this one? That might help isolate the problem.
Alas, there doesn't seem to be much interest in this particular machine but I think my "Isaac" is a "way cool" bad boy dude and intend to make a small pieced quilt with the hand crank "for fun". Otherwise it's my "in case of power failure" machine here at my place in New Mexico. Eventually, I'll take the motor and controller to someone who knows about such things. As an aside....I wonder if any of the "vintage" experts here on the Board who are reading this thread would be able to give me a source where I could get a "real" spoked hand wheel and hand crank? If so, please PM me! Thank you!