it also has to do with the tension. If your tension is off on the bottom (too loose) it shows on the top. And vice versa, top looseness shows on teh bottom. Play with your tension on the bobbin first, then adjust the top. This is DSM? or long- or mid-arm? Different threads also require different size needles. So you have some experimentation to do...Keep notes (though I don't--do as I say and all that *G*)