older model white machine

Incorrectly adjusted upper thread tension. Make sure the thread is properly threaded through ALL guides and properly between the tension disks and try moving the tension control dial so it's putting more tension on the thread.

Not enough tension on the needle thread, most commonly caused by not lowering the presser foot before you start to sew.

Or you may have bypassed the tension disks when you were threading the machine. Raise the presser foot and rethread, making sure that the thread goes right between the tension disks.

Or the tension disks may need cleaning by raising the presser foot, unthreading the machine and "flossing" gently between the tension disks with a piece of soft lint-free fabric.

HTH

Also burrs on the hook may "grab" the upper thread kepping it from being pulled back up.

Jean

"Kelly and Robert" a écrit dans le message de news: snipped-for-privacy@corp.supernews.com...

Another classic is not putting the bobbin case all the way in on a vertical bobbin machine - the thread catches on the latch and makes a lovely big mess in the shuttle mechanism, requiring much use of tweezers, head torches, swearing... ;)