I had difficulty like yours. Just a straight line of thread and loops from the top. I didn't change any tension, but cleaned all around the bobbin, made sure the thread in the top and bottom were the same, reinserted the bobbin, rethreaded the top thread...that did it! I think I was probably using two different weights of thread. At a class by Nova Montgomery with my FW, I couldn't get the tension correct. Nova came and did something with the tension and it was a bit different for my machine than on most FWs. So if it can't be adjusted by all of the above hints/helps, it may be time for an expert on your machine.