oldsewandsew,
Thread looping on the top is controlled by the bobbin tension. Thread looping on the bottom is top tension problems.
I think it's ArchaicArcane that has a method of setting the top and bottom tensions on her blog. Miriam has several threads about tension problems here too.
What I do is fill a bobbin, put it in the shuttle and then thread it. Then I hold it by the thread letting the shuttle dangle on the thread. Give a little bounce on the thread. If the shuttle drops just a bit it's good to go. If not I loosen it's tension an 1/8 th turn and try again.
If it drops a lot I tighten it an 1/8 th turn and repeat the drop test.
After I get the shuttles where I like them I work on the top tension.
Joe