Big loops on bottom stitch

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/

Check your stitch sample. The loose stitches under the fabric--are they actually top thread???? Usually,stitch problems under the fabric is a result of a top thread problem. In this case, it could be bird nesting.

Remove the top thread from the machine.
Install a brand new needle.
ALWAYS RAISE the presser foot.
Rethread from the beginning.

Sewing Machine Thread Bunching Up Here Why

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

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

have you tried changing the needle?
have you tried adjusting the top thread tension?
it might be the needle and the thread are not compatable,, the needle may be to light for the thread.
if the suggestions don't help, sew on the sewing machine till it makes the loop and then stop the machine and take it to the repair man and let him see the loop and then ask him why it's making the loop.

here is a link for a manual for the machine
http://ifixmachines.com/index.php?page=shop.product_details&flypage=&product_id=1540&category_id=1575&option=com_virtuemart&Itemid=54&vmcchk=1&Itemid=54

try changing the needle--use one that is correct for the fabric being
sewed
the top tension adjustment for the bottom loops
make sure the bobbin is turned the right way in the bobbin case
make sure the top thread has not come off the thread take up lever

type in your browser chain stitch machine & it will bring up website
that have them

Well is your machine skipping stitches? "Not looping" does that mean not creating a stitch? To adjust your bottom stitch you usually adjust the top tension regulator. I can try to help you more in detail check out my forums http://www.sewingmachineryrepair.com/forums/index.php

Have you tried to re-thread the machine? Check to see if the thread is in the take-up lever. There also might be a piece of thread or lint caught between the top tension disks.

FYI---- Loops on the bottom-- problem is in the threading..
Loops on the top--- problem is with the bobbin.

Looping on bottom:
Great description, that helps a lot. Big loops are actually easier to solve usually. 1st know this: Loops on bottom means the top is too loose or the bottom is too tight. With loops that big its probably the top is too loose. 1st look in tension disks, there is likely a chunk of thread in there. A toothpick is handy to dig it out (the flat kind) 2nd make sure that the thread is getting between the disks when threaded. 3rd Make sure the thread is in the take up lever (the thing that moves up and down in front and not the needle bar or any part of the needle bar.) If neither, then the bobbin case could have a burr on it and the thread is hanging on that burr. Also the bobbin case may be in wrong. I hope this helps
Kent581