Originally Posted by
Peckish
A mess on the bottom is not a bobbin issue, it's a top thread issue. There are any number of things that could be causing it. Check the manual carefully and make sure the top thread is threaded correctly. Make sure nothing is impeding the thread path as you sew. Try adjusting the top tension tighter. Make sure your thread size is matched to your needle size, maybe try a larger needle. And this one is sort of obvious, but we've all done it - make sure the presser foot is down.
As others have said, maybe it simply needs to go in for service. A good service tech will take time to show you things and answer all your questions.
Yes, yes, please follow this advice, a mess on the bottom is an upper threading problem, I suspect the upper thread is not getting into the tension disks properly. Are you threading with the pressure foot up? If you thread with the pressur foot down the thread can not sit in the tension disks.