If all of the above doesn't work...........
It actually sounds like a bobbin case problem. Does it snap in and seem to fit right? I would take the bobbin case somewhere and check to see if it is the correct one. I'll try and find a pic of one and send you the link.
http://www.amazon.com/Singer-Bobbin-.../dp/B003AJUNJ6
There is also a yahoo groups for featherweight owners. If you join (its free) you can post questions and read other posts to find answers to other questions.
http://groups.yahoo.com/group/featherweight/