Per my quilting teacher- bad tension can be caused by the top thread not being caught in the tension mechanism correctly. To solve -rethread the top thread with the presser foot up. after threading the needle drop the presser foot and gently pull the top thread. If the needle bends then it is threaded correctly in the tension plate. If the thread just pulls it is not correct and needs to be rethreaded. Teacher said the the tension is like too plates back to back. When the foot is up the plates are apart and when the foot it down then the plates are together and that is what controls the tension.