Surfer:
I just took my bobbin winder apart and took a bunch pictures and will post them if you need, but I think I discovered a couple of things to check.
First off did you take yours completely apart?
If you did you found two cupped washers. They are not the same. One is thicker than the other. The THIN one goes behind the toothed wheel with the heart shaped cam.
Also the screw that holds the cam on is "etcentric" and is used to adjust the tooth engagement to the screw drive (on the tire).
So make sure to use the thin washer, adjust the cam to just engage and then tighten the nut on the back. That should take care of it.
Let me know how it turns out.
Dan.