Bobbin knots up

Not knowing the brand and model of your machine makes diagnosis difficult. In most machines that have the bobbin case inserted from the front, you can try releasing the bobbin case and removing it. When my machine jams, removing the bobbin case releases all those threads that are twisted and knotted inside that are "holding the needle captive."

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The carrier and bobbin are removed. Place the thread in the carrier with the thread dispensing counterclockwise. Place the thread between the metal pieces (tension). let the carrier hang from your finger and bob it slightly. It should extend one inch. If it doesn't then you can adjust it by turning the small screw slightly until it does what I said. Now, replace this assembly. The top tension you can start at three. The sewing should be an even pull between the upper and lower thread. If the thread knot is in the center of the material it is right. If the knot is under the material then raise the upper tension. If the knot is on the upper material then you should lower the upper tension. The key is to start with the bobbin tension correct and adjust the upper tension until the knot is in the center of the fabric

First check in the bobbin area for lint, bits of thread wrapped round parts.

Then make sure your needle is oriented and inserted fully.

Also when starting a seam be sure to grasp both of the threads and hold them as you start to sew.

If you still have problems, make sure your thread and needle are suitable for your fabric.

Since you don't really say where it knots and breaks ... it could also be a damaged needle plate.

What you have going on is probably a bobbin problem. The knots are referred to as birds' nests and happen usually happen when your bobbin thread gets caught on something in the bobbin area. To be certain it's a bobbin problem, change your needle. Even if the needle looks fine, it could be just slightly bent and still look fine to the naked eye. If that doesn't solve the problem, take the fabric out of the sewing machine and turn the machine wheel by hand. Watch what happens thru the plastic window in the bobbin area, or if you don't have a plastic window leave the bobbin covering off. Is the thread catching somewhere and causing a bunch of thread to gather in the bobbin area? Be very careful when investigating in the bobbin casing/area-it's easy to chip things in there! Often times, a piece of something falls in there and can be pulled out with tweezers. Just as often, the bobbin casing is slightly tilted and needs to be straightened or has a chip in it and needs to be replaced. You can normally get a replacement on eBay, searching with your machine model number. Also, check out SewVacUSA. If you need help replacing the bobbin casing (it's easy, you just need to be careful), or if these solutions don't work, leave me a comment. I check back daily, so I'll get back to you within 24 hours normally. Leave me as much detail as possible and I'll do everything I can to help you!

Could be a few things. Absolutely minutely check that the top thread is threaded properly. Otherwise, it could be: Old thread. incorrect thread for the material. wrong size or blunt needle. or incorrect tension on needle I had this problem and I was missing a part of threading even though I have been sewing for years. :)

Get out the manual and refer to the maintenance section for cleaning the machine.

Especially the bobbin area. You want to make sure the area around the bobbin case is free of lint and thread.

Use a new bobbin and re-thread the machine, with the presser foot UP.

Install a new needle, again according to the directions in the manual. Installed incorrectly can lead to mis-stitching.

If the problem persits, the timing may need adjusting.

This should be done by the sewing machine tech for Kenmore.

Sewusa.com has a guide for this in the repair section, but you could end up with more problems.

upper tension wrong or machine not threaded correctly.

Are you sure you have the bobbin the right way round in the holder....when you look at the bobbin and tug the thread, the bobbin should move clockwise.
Pull out the foot pedal and use bsr2 with the start/stop button.
Bring bobbin thread to top of work before starting to sew. This may help knotting problem

Thread test
Test your thread quality to start, thread your machine and LIFT the presser foot (this opens the tension disks). Pull your top thread straight back. If you feel no tension no mater how much thread you pull, your thread is good. If that your machine passes that test, then let me know, we can go to step 2. If not, try different spool of thread, same test until you get a smooth pull (tip: always check your thread this way when you thread your machine)
Step 2:
Pull on your threaded bobbin thread while it’s in the machine. Does it pull smooth and even? If so, go to step 3. If not, try a new bobbin (bobbins get bent or distorted if wound too tight).
Clean thoroughly in the hook and bobbin case area and oil 1-2 drop is all.
Thread knotting on the bobbin can be a lot of things but here's some guidance:
Tension:
If the thread is loose on the bottom of the fabric, it's actually the top thread is too loose. Think of 2 little elves playing tug of war in your machine, one on toip and one underneath. If you have loops on bottom, the top needs to pull harder (tighten top tension)
Jamming bobbin case:
If it is damaged from turning out of place once, it could have rough spots on it that makes the thread hang on it, and keeps making it turn over and over. Use a finger nail board (fine sanding) and smoothall rough spots. Then reset the bobbin case taking care to put the notch in the bobbin case in alignment with the proper spot in the machine (basically 5 o’clock) when looking at the round area where the bobbin case goes.

My machine does the same thing. Unplug the machine, and open the bobbin case. I would bet that you have "orphan" thread still sitting in the bobbin area that is bunching up the new thread.
Your bobbin area should be opened, cleaned and well oiled to ensure that no loose threads are sitting in there waiting to create "tension" with you and your machine.
I have found that when I have not cleaned out the bobbin area, there are loose threads, lint and fibers left behind from other projects that I have been working on.
Get a new can of compressed air, and blow out the lint, and left behind stuff, and see if that doesn't fix your problem. If it's been a while since you have taken it in for a "tune up", it should be done if you use your machine often. Happy Sewing!