Generally, loops on the back means your top thread tension is too loose. You might try turning the dial incrementally and tightening it.
This article might help.
http://www.threadsmagazine.com/item/...nsion/page/all
At the bottom of the article is a list of possible reasons that might be affecting your tension:
Incorrectly threaded machine
incorrectly wound bobbin
dirty machine
damaged parts
needle/fabric/thread factors
For quilters, the problems are usually incorrect threading, a dirty machine (even something as small as a tiny piece of thread caught in the tension discs will throw off the tension), or the tension needs to be adjusted.