Perhaps it is not tension but the stitches that are too tightly together. Try lengthening the stitches up a notch and using a walking foot if the fabric is heavier than usual. Or it could be the top thread is caught on something while threading the machine. That happened to me once. The thread wound around the spool on the last bit of winding a bobbin and I didn't realize it. That caused a drag on the thread and a top curl of the fabric.
Last edited by RedGarnet222; 05-26-2013 at 06:01 AM.