My sister has a Tin Lizzie, and she has had some tension problems like you mention. Now, I hope she reads this thread, but she is teaching a workshop today and may not have time to be on the computer....so let me pass on what I think I know...that may help. When she is putting the bobbin in the bobbin case, there is a little thing she calls a pig tail that she makes sure the thread...oh, not sure what the thread does....wraps around maybe or goes thruogh? If that makes any sense, good. If not, just ignore it.
Dina