With the tread binding it might be the upper tension or the bobbin tension. On a model that old there should be a very small screw on the side of the bobbin casing. Trying turning it about 1/16 rotation to loosen or tighten the bobbin thread.
But, it sounds like that you may not have it threaded right on the top side. I have been sewing on the same machine for 40 years, I have a brand new quilting machine, but I keep the old one for making garb and sewing the harder stuff. \
Let me know if I can be of help.