Hope the cleaning and rethreading worked. Don't forget to oil the machine, too. One more suggestion is to check that a broken piece of thread isn't stuck in the tension gear before you start adjusting. Even a tiny piece can clog the gear and cause a strain on the thread. If everything else fails and you must adjust the tension, make a note of the number it's on before you start, adjust in small increments and sew after each adjustment. Hope it works.