I don't know the particulars on the 400 series machines enough to tell you how to fix it. Does the tension release when the presser foot is raised? Also what kind of thread are you using and how is it wound on the spool? That can have an effect on how the thread feeds too. It might be Archaic Arcane's blog that has a great write up on the different ways thread is loaded on the spool, the effect it can have and what to do about it. Someone here will correct me if I'm wrong I hope.
Rodney