Originally Posted by
FlippingHades
Definitely check 2 things about the needle -- first, make sure it's inserted correctly! With industrials you can rotate the needle 360 degrees; there's no flat to keep it inserted perfectly. I've inserted one backwards before and spent long minutes going crazy until I realized my mistake.
If the needle's inserted correctly, try changing it - a dull needle can cause no end of headaches.
also if you use size 90 bonded thread it doesn't like going backwards too much on a drop feed machine the thread will wrap itself and come apart I have also had issues with bobbin cases being old and not keeping the thread tight enough
another thing could be that you machine is just dirty when lint and stuff build up underneath the bed plate it can have all kind of mystery issue
now I am on a tangent