http://www.quiltingboard.com/vintage...g-t182255.html
Since it is a 306 it could be the wrong needle or someone might have tried to time it to work with a more modern needle. There is some discussion on that on various places on the net - some info on here:
http://www.quiltingboard.com/picture...c-t162425.html you might also need to clean up any dried oil on the tension area ask me why I know that...