Miriam,
Besides being "early junque", I think the design is off or flawed in some way. I can think of nothing more annoying than a machine that surges as it tries to make stitches. None of my other cam ( built in or removable) machines do that. Since all three of them do it, it's got to be something to do with the design.
I'm gonna play with the one I have as time permits, but it will never get used seriously.
Joe