Stitches looping up on bobbin side of fabric - Necchi Sewing Machines

Looping stitches can be caused by a few different factors. Make sure that your machine is threaded correctly. If the top thread or bobbin thread is improperly threaded it can cause looping stitches. ... Loose thread tension will create loose loops of thread that can cause the needle to catch and create more of a mess.
https://www.madeirausa.com/services/troubleshooting/fabric-puckering/

You are getting a thread mess under the fabric? Frequently, this occurs because the top thread is not fully seated in the tension disk.

Install a brand new needle.
Remove the top thread from the machine.
ALWAYS RAISE the presser foot and rethread the machine from the beginning.
If necessary, adjust the top tension so the top and bobbin threads meet in the middle of the fabric.

Sewing Machine Thread Bunching Up Here Why

Birds nest under the fabric big loops of thread top side looks good...

TIP Avoid Thread Bird Nesting with these Four Tips Stitching Sewcial

Troubleshooting Thread Nesting Sew Toot

On any machine, the lower - bobbin tension is adjusted with a small screw driver, used on the very small screw on the side of the bobbin. "Righty, tighty, Lefty - Loosy." If you stitch an inch of fabric, and the bottom loops come up, then... tighten the bobbin holder. If the loops pull down, loosten it.

Check your stitch sample. The looping under the fabric is most likely the top thread. If so, this is call bird nesting or thread nesting. Most common cause is the top thread is not completely seated in the tension disk.

Remove the top thread from the machine.
ALWAYS RAISE the presser foot and rethread the top thread.
Set the top tension at the midway point (this can be tweaked later).

Test your stitch. Increase or decrease the top tension until the top & bobbin threads meet in the middle of your fabric.

What causes Bird Nests Superior Threads

Is it actually the bobbin thread that loops or is the loop appearing on the underside of the fabric as you stitch? If it is a loop under the fabric, that's usually an indication it is an upper thread issue. Thread irregularities that appear on the topside of the fabric are generally bobbin related.

First thing to try is installing a brand new needle. Verify it is the correct needle for the fabric and thread being used.
All About Needles
Sometimes, the fabric being stitched will "grab" the thread and hold it for a second before releasing and will cause a loop. In this case, a needle with a larger scarf and eye may be helpful.

You might also open the upper tension as much as possible, RAISE the presser foot and run a piece of UNwaxed dental floss through the tension disk a few times to clear out any gunk that may be stuck there. A piece of pearl cotton dipped in rubbing alcohol and squeezed moist/dry will also work.

Remove the upper thread. RAISE the presser foot and rethread the top thread from the beginning. Use only fresh, good quality thread--NO old or bargain bin variety! Try using the same thread in the top and bobbin. Make sure the thread is firmly seated in the tension disk and the thread path is correct. Check that there are no burrs or snags in the thread path that could be catching the upper thread. Especially, check that the thread is not catching on the spool "slit" that holds the thread when in storage. Every time the thread navigates around the thread spool, it could be catching on that slit just enough to cause a loop.

Try changing the bobbin. There could be something amiss with the current bobbin--could be nicked or could even be the wrong bobbin for the machine. Also, make sure the bobbin is loaded and turning the correct direction in the machine.

Set the upper tension to the midway point. This is usually the starting point, although it will probably require some tweaking. Test your stitch and adjust the tension so the upper and bobbin threads meet in the middle of the fabric. Neither thread should dominate one side of the fabric or the other.

Understanding Thread Tension Threads

Last thing to try is a different presser foot.

If you still have the intermittent loop, you might want to take it for service. Could be a problem within the tension disk.

If the bottom thread is tight there should also be loops on top and this means that the upper tension is too tight.
Get out your manual (http://www.singerco.com/uploads/download/1198_8763-efs.pdf) and turn to page 24. Under "ADJUSTING TOP THREAD TENSION" it tells you that if you're having thread tension issues, change the tension control dial on the top of your machine from auto. It also shows you a diagram with your problem illustrated on the right side of the page. The bobbin tension is set at the factory, so all tension problems can be solved with top tension adjustment. Set it manually and if it loops on top, loosen the tension a little. Test again. Repeat until loops are gone.
Using different colours on top and bobbin and a contrasting fabric (e.g. black top, white bottom, light blue fabric) means you can easily see what's happening. A perfect stitch is when you see exactly the same stitch pattern on both sides of the fabric. On top, the bobbin thread colour appears between stitches as a tiny dot and on the bottom, you see the top thread dot between stitches.
If it's impossible to get the tension right, take it to a technician, because it's a sign that the hook timing needs attention.

Hi Sylvia,
Your problem is an un-matched tension of the threads. You mentioned doing an adjustment recently. That is the problem area.
If your bobbin thread develops loops on the top side of the fabric, you need to tighten the bobbin tension.
There is no easy method for this and you will have to do it slowly -
tighten, test, re-tighten, test.... until you get a near perfect stitch.
I haven't come across a portable device specifically designed to set thread tensions.

Loops stitches on the underside is typically from the TOP tension being too loose, however it can also be the bobbin tension is too tight, or a problem with the needle. I would check them in that order.

Hold the bobbin thread and let the bobbin dangle. A slight shake of your hand should allow the bobbin to move downward (lets more thread out) but not so much that it just drops to the floor. When you put it in again and try sewing look at the top stitches. Do they look overly tight? THen the bobbin tension is too tight. The stitching should look the same top and bottom with no loops.

If both tensions seem to be alright check to see if the needle is: 1. the right size and type of the fabric 2. not bent

That should fix your problem :)

1. Loosen needle screw & insert needle with shank's flat side facing front of machine. Push needle in all the way, then tighten screw to hold needle in place.
2. Install a fully wound bobbin by loosening bobbin nut & placing bobbin on top. Re-attach bobbin nut & tighten. If standard thread spool will be used, then attach spool pin to bobbin shaft & place thread spool onto shaft. Attach white spool cap on end of thread spool, then tighten. Bobbin/spool should unwind facing forward toward needle.
3. Bring end of thread through thread guides & over tension control. Pass end of thread through needle eye, from back to front, & pull it out about two inches.
4. A spring pushes pressor foot onto fabric that is being sewn, so lift pressor foot & place fabric underneath.
5. Turn large handwheel on side of machine (handwheel can be turned in either direction) to raise needle arm to its highest position.
6. Holding the Handy Stitch in place with your right hand, press on power switch & begin sewing. Guide fabric (being sewn) with your left hand.
7. To end this sewing session, turn off power. Turn handwheel to raise needle to its highest position. Carefully pull out about three inches of thread through needle & snip, then lift pressor foot to remove fabric. Turn fabric over & loop needle threader through last stitch. Place end of thread from underside through eye of needle threader, & pull to loop through. Pull to tighten and snip end of thread.

Loops on the bottom of the fabric direct the problem to the top thread. Rethread again and make sure the thread goes through the tension discs. Lift the foot, because this is what opens the discs. When sewing and the foot is down, the discs should be closed and thus giving the upper thread the tension it needs.