"You're not holding your mouth right", got a big smile from me! When this happens to me, it's because my top tension dial has moved (on it's own), all the way down to "0". I have to be soooo careful about touching it. Just a "glancing blow" will cause my dial to move. I've taken it in to have it fixed and it's better. It used to move on it's own.. just the action of the machine sewing would cause it to move. So... I'd check your top tension dial.