Juki 555- Why do I have to set top tension so high to form a good stitch?
I am sewing canvas with an old Juki DDL 555 and I have to make the top tension so tight to get it to pull the bobbin thread to the center of the cloth that I am almost at the point of braking the thread. The bobbin tension is as loose as I can make it. I am using T-135 polyester thread with a size 20 needle. With two layers of canvas it just works but I want to be able to sew 4 without the tension so tight. The needle looks big enough but I am ordering more to try.
What else could be stopping it from pulling the bobbin thread to the center?