Thread loops on back using quilt stitch

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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A #16 needle seems pretty big for FMQ. Are you also getting pin holes in the fabric? Try using a top stitch, embroidery, or metallix needle.

Eyelashing is often a result of moving the fabric too quickly. Try speeding up your sewing speed or slow down the fabric movement. The object is to get the stitch speed equal to the fabric movement--and keeping it consistent. I tend to make swirls too fast which causes eyelashing.

It could also be tension. Be sure to ALWAYS RAISE the presser foot when threading the top thread.

What causes thread eyelashes when sewing

LOOPS Tension or Speed

It could be a variety of things. Be sure you are using a brand new sharp needle (try a topstitch, embroidery, or microtex needle on woven cotton). Be sure the needle eye is large enough to accommodate the thread weight. Different needles have a different scarf (the groove that is on the back of the needle that runs up from the needle eye). A larger scarf will protect the thread and keep the thread from hanging up on the fabric when the needle is withdrawn from the fabric.

http://www.schmetzneedles.com/all-about-needles/

Also, the upper tension may be too loose if it is still showing loops under the fabric.

Another cause is the fabric being stretched too tight on the frame causing trampolining.
http://www.kimmyquilt.com/tensioning-the-quilt.htm

Frame Quilting

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Be sure you are using a brand new needle.

Remove the thread from the machine.

ALWAYS RAISE THE PRESSER FOOT and rethread the upper thread from the beginning. Make sure the thread path is correct.

Verify the bobbin is installed and turning the correct direction in the bobbin case and that the bobbin thread is threaded through the bobbin tension mechanism.

Set the upper tension to the midway point between high & low number--this may require some adjustment for your particular machine.

Pull the bobbin thread to the top of your sewing project before beginning to stitch.
How and Why to Bring up the Bobbin Thread

Re-test your machine on a scrap quilt sandwich (make sure the walking foot is installed correctly and that the presser foot is lowered when beginning to stitch).

Consult the owner's manual for instructions for presser foot pressure. The pressure may need to be adjusted because you are dealing with a sandwich that is thicker than regular fabric.

You may also try changing the type and size sewing machine needle you are using. Using a Top Stitch or Microtext needle will help the needle to penetrate the fabric sandwich easier. A Top Stitch needle has a larger groove to protect the thread as it pierces the fabric which helps prevent looping.

Also, verify the thread is not too small for the needle's eye.

All About Needles

https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=2&ved=0ahUKEwil1tu2mb3PAhVR6mMKHUlvB_4QFggoMAE&url=http%3A%2F%2Fwww.schmetzneedles.com%2Flearning%2Fpdf%2Fschmetz-needle-chart.pdf&usg=AFQjCNHTR52AmqwzvyCjbXmD5Ch52Va5_Q&cad=rja

What kind of thread are you using. The most often problem today is that the thread is too thick for the size of needle. Try using a Metallica size 90 or a top stitching needle size 90
if the thread is a cotton type or a quilting thread it is often to thick to travel easily through the eye of a needle quickly to form a good stitch.

Could be several things.

First, install a brand new needle, perhaps a top-stitch needle will work better because it has a groove in the shaft that protects the thread. Make sure the needle is the appropriate size for the thread you are using--a needle eye that is too small will cause the thread to hang or shred. When the needle penetrates the sandwich, the top thread forms a loop. If the eye is too small, the thread will not come back up through the sandwich, leaving a loop under the fabric.

Remove the top thread from the machine.
ALWAYS RAISE the presser foot and rethread from the beginning.
Set the top tension to the midway point and retest your machine on a quilt sandwich made of the same fabric layers as your project.. Tension problems are more evident when sewing multiple layers of fabric, so tweak the tension until the top and bobbin threads meet in the middle of the sandwich.

I don't believe you will have to adjust the bobbin tension, but in case you do, be very careful. Mark the tension screw setting FIRST so you can reverse any changes you make. Bobbin adjustments are made in very SMALL increments. Because I tend to use a lighter weight thread for my quilting, I have a specific bobbin case that is adjusted for my quilt thread and I keep my other bobbin for regular sewing. Then I don't have to keep adjusting the bobbin tension when going from sewing a quilt to something else.

Some machines do better with certain brands of threads than others.

Adjusting Sewing Machine Tension to Prevent Problems

12 wt thread generally will not work well in the bobbin...


"Aurifil 12wt Thread
Aurifil 12 wt thread is ideal for hand quilting, big stitch hand quilting and machine quilting. 12 weight thread creates a more defined and often primitive look. It's great for designs that use a longer stitch length if using a machine. When machine quilting with 12 wt thread, use 40 wt in the bobbin, increase your stitch length, lower your tension, use Topstitch size 90 needles and stitch slowly."

You didn't specify your machine brand or model which may make a difference in setting it up.

Using the machine with it in a cabinet or flat extension plate is necessary to allow easy movement and keep the fabric flat. Make sure that you have enough layers of fabric to give stability to the stitch.

With the needle bar in its highest position and the presser bar up, install the foot on the machine. Lower the feed dogs (if your machine has the feature), set the pattern for straight stitch and LOWER the presser foot. Hold the upper thread with your left hand and make one rotation of the handwheel with your right hand. Pull the top thread and the bobbin thread will come up with it. As you stitch, move the fabric in an even, fluid motion. This will take a little practice, but it will get easier with time. Make up some "sandwiches" to practice with. A sandwich is two pieces of cotton fabric with batting in between, usually six to ten inches square.

Your upper tension may need to be adjusted a number or two up or down. Experiment!

Might be that you need to lower the tensions quite a bit, you'll have to juggle with top and bottom tensions though, and experiment for just this operation with the Sensormatic.

Try oiling the hook if you haven't recently.
Check you needle plate and hook for damage, they may need to be buffed or sanded smooth.
Check your upper tension discs for lint and double check your upper thread path (proper threading).
There are other things like hook timing, needle clearance or broken check spring that may be wrong but you need a technician for those things.
best of luck!