The threads under my fabric are ''bundling up''

Be sure stitch is in between the two fabrics when straight stitch. Adjust tension until stitch is between top and bottom fabric. Use different color top thread to make it easier to see. Once tension is correct sewing straight, switch to zigzag.

Remove hook race and bobbin. Clean area with vacuum.
Replace needle.
Try different thread and fabric.

Quilting is a bit more finicky than regular sewing. Be sure to ALWAYS RAISE the presser foot when threading the top thread. FWIW, I use a separate bobbin case for FMQ that I have tightened the tension to keep the bobbin thread from coming to the top of the sandwich, but I tend to use a finer thread for quilting so adjusting the bobbin takes care of it. In your case, however, it sounds like the top thread is staying under the fabric. I would try tightening the top tension. Also, install a brand new needle--a top stitch, embroidery, or microtex needle seem to work well for me. Test well on a sandwich made of the same fabric and batting and get it adjusted well before sewing on your quilt. Sometimes sewing speed will affect stitches under the fabric, or even on top.

5 Free Motion Quilting Problems and How to Fix Them

Correcting Sewing Machine Tension for Free Motion Quilting NQC

LOOPS Tension or Speed

https://www.generations-quilt-patterns.com/machine-quilting-thread.html

https://www.generations-quilt-patterns.com/sewing-machine-tension.html

https://www.generations-quilt-patterns.com/machine-quilting-tension-problems.html

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try changing the needle it could be blunt

also make sure the top thread has not come off the thread take up lever

clean under the needle plate and in the bobbin are for lint

Is it really the bobbin thread that is bunching under the fabric, or is it really the top thread that is creating loops and "bird nests" under the fabric???

Rethread your upper thread. BEFORE you thread the upper thread, be sure to RAISE the presser foot. This releases the upper thread tension disks so the thread is firmly seated in the tension disk.

If it continues to be a problem, then the upper tension needs to be tightened. Adjust slightly, then test. Repeat until the upper and lower threads meet in the middle of the fabric.

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Sounds like it is still not feeding smoothly, Try putting some clear tape on the bottom of the foot and tissue paper under the leather. Leather is tricky sometimes.

Needle/fabric/thread combination is wrong. hope this helps

I think you are saying no stitch is formed also referred to as the needle not catching thread. Below offers a variety of diagnoses and solutions which are straight forward.

Sewing Machine Needle Not Catching Thread

Below is general advice quoted from 6 common sewing machine problems solved:

Skipped stitches are usually due to a bad needle. The needle may have become damaged or bent by sewing material too thick for the needle, forcing material through the feed dog, or hitting a straight pin. If the problem seems to be consistently reoccurring, it may be due to forcing the fabric. Sewers should allow the feed dog to pull the fabric and only use their hands to guide the fabric through the feed. When sewing knitted fabrics, using a stretch needle can help prevent skipped stitches.

Below is a video showing how thread is hooked into a fabric:

Sewing Machine Anatomy How Stitch is Made

You may have a jam under the needle plate. Take it off and have a look.
It is often a simple case of one of the threads not passing through the tension discs correctly. Try re-threading upper and lower, making sure the presser foot is up at the time.

Are you sewing a fine material? Sometimes fine fabric gets pushed down through the universal needle plate hole which is slightly elongated. If this is the case you need a straight stitch needle plate. You cannot do zig zig or anything other than straight stitch with this plate.

If re-threading does not do it and you do have a soft fabric, try popping some freezer paper or similar under the first few centimeters of sewing before buying another needle plate, it might work.

This is a very common problem with really lightweight fabric and can often be cured (if doing straight stitching) by using a straight stitch needle plate and foot. The wider needle plate and foot openings on newer machines give the machine/thread a wider area to pull the fabric into the machine. By using a straight stitch plate/foot you remove the wide opening, eliminating the majority of the problem.

Also - try using a specially coated needle (Teflon or other non-stick finish). The thread feeds more smoothly through the needle and the needle more smoothly through the fabric, causing less drag into the needle plate opening.

Hope this helps. Don't hesitate to respond to this if you have further specific questions. We're always happy to help

Happy stitching,
Kim & Linnette
www.sewingexpressions.com

it sounds like you might need a new bobbin case to me try that and see if the issues you are having stop hope this helps