a careless sewer and a FW don't go well together. provided machine is oiled and free, and the motor runs strong with the belt off, 99% of it comes down to correction needle facing, bobbin case ltched into the noth uner the needle plate, O THReAD JAM behind or around bobbin case as you said, bobbin in and latched. You can remove needle plate to help make sure, but then be sure bobbin case finger goes in the notch...