Bobbin thread tangles

Is this machine new to you or have you had it awhile and it worked fine before?

Are you sure it is top thread?... use a similar but contrasting color for top thread to be sure.

Do you have the manual to be sure you are threading it properly?

See following video on threading the Lydia 3.

https://youtu.be/wVifJVsrO80

Comment below for further assistance.

Yes quality of thread could definitely affect sewing, as will a blunt/old/wrong size needle for the material used. Also must have same thread in bobbin and needle also corect thread and needle size for material sewn plus correct tension for that material too. Could be lint or tangled threads underneath needle plate too.

when you put the bobbin in the carrier make sure you have about 6" of thread out
next adjust the needle thread tension right up

The problem most likely is not the bobbin. The problem is the top thread. If thread is knotting, tangling under the fabric, it is a top thread problem.

Remove the top thread from the machine. ALWAYS RAISE the presser foot and rethread from the beginning.

If there are still thread clumps under the fabric, you will need to increase the top tension. (The extra thread appearing under the fabric is excess top thread hanging up under the fabric.) You may need to keep adjusting the top tension until both top & bobbin threads meet in the middle of the fabric.

....

Perhaps a manual would be helpful:

http://freenecchisewingmachinefiles.weebly.com/

Necchi 542 and 544 Lydia Sewing Machine Threading Diagram

Necchi Lydia 3 Models 542 544 series Part III Stitches Buttonholes

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Necchi 544 manual free

Instruction Manual Necchi 544 Lydia 3

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try a different bobbin
make sure the bobbin in turned the right way in the bobbin case
also the machine may have a timing problem, and having it checked to would be a good idea.

These machines were prone to cracks in the bobbin case (which are exorbitantly expensive to replace) and sticky pattern camstack sliders. I would take it to a repair person familiar with the Lydia. I wouldn't spend much to repair it, as you could improve vastly with even an inexpensive machine from Sears. The new Necchi machines are Taiwan imports and are not related in any way to the old Italian Necchi machines.

if the thread under the fabric is a matted mess
1.the needle thread tension is to loose
2.needle is either to heavy or to fine for the thread
3.check to make sure the thread isn't off the thread take-up lever

There is a site that has instructions with how to thread the machine properly. Click here for the www.sewusa.com threading section