only adjust the tension with the presser foot down or the thread will just pull out freely - your manual is your best friend keep it near by and look at it frequently
There are lots of reasons the tension doesn't do what it is suppose to here is a trouble shooting list might help:
http://www.quiltingboard.com/vintage...s-t170748.html
It is an old one - you may have to cut and paste if the links don't go anyplace