Hey Joe, just some thoughts. . .
- perhaps the cams giving you trouble have a bad history -- like someone trying them out in one of the 600 series or another cam machine so they aren't right.
- regarding the bobbin jams -- I've noticed a couple things that triggered that (besides those discussed already). If I had short leader thread (both top and bottom) when I started sewing, it sometimes dropped into the bobbin and the first stitches became a rats nest. Got into the habit of holding onto the thread as I started. Also found that if I didn't stop when I did the back stitch to start before I charged forward, I made another mess. As I got older and slowed down a bit, both the machine and I behave a bit better. Not winning too many races with the car anymore either.
Lastly, you probably have already checked this, but I did have to replace the bobbin holder after my daughter created a nice jam. She got "stuck" and yanked. I cleaned it up but still had some problems. The new holder has been working for 20 years now.
Not sure if any of this helps, but who can tell? Good luck!