Help me fix my sewing machine!

[RooibosWithMilk]

Hello knowledgable sewing types :)

I have an old Jones sewing machine which I bought on ebay last year. It usually works fairly well, but occasionally does something weird (and hard to describe) where it catches for a moment, there's a whirring sound, a large amount of the top thread is pulled from the spool and a huge loop is created underneath the fabric. Usually I keep sewing then just tie up the loop and cut it off afterwards (professional I know...) but recently it's got worse - creating a loop every few stitches, then they get all tangled up and stop any sewing progress whatsoever.

Any ideas what could be causing this? It seems like maybe the bobbin sticks for a moment but I'm not sure. I've tried cleaning and oiling the machine, and I've also fiddled with the upper thread tension - both had a discernible effect but unfortunately didn't stop the weird pulling/looping problem.

Any ideas of what might help?

(I'm annoyed because I'm half way through sewing a pair of trousers for my baby, due on December 30th, and I really wanted to get them finished before he/she comes along!)

Could be the thread tensioning... Sometimes it is higher on top than below and that causes ruching like that....

If you find an answer, I'd love to know, as my Brother despite lots of loving care, does it too!

it could be the bobbin itself - run your fingers around it to check for ant scratches or dents.

Thread looping on the bottom of your fabric is usually caused by little or no top tension or too much bobbin tension. Try experimenting on a left over piece of the same fabric.

Another cause is thread or lint caught in the top tension or using cheap thread that sheds lint and doen't flow through the needle smoothly. Make sure the machine is threaded correctly and that the thread hasn't jumped out of the tension discs and that no thread or lint is caught. Ensure you are using the same thread top and bottom.

Change the needle as it might be blunt or bent or have a scratches. Also check the bobbin (as already mentioned) to make sure it is evenly wound and does not have any scratches in it. Maybe change the bobbin too - it might have become slightly warped.

It's so FRUSTRATING isn't it?
And good luck with baby day

goes off to check all the tips out herself