sometimes on the bobbin, there's a whiplash effect that causes loops under the fabric. they have these little teflon discs , very pricey, that you slip into the bobbin case and lt allows just the right amount of friction to keep that from happening. then make sure that the bobbin is facing the right way. the bottom loops should disappear. then if you get the upper tension right, which is now easier, you're ready to rock'n'roll.