L-344 loose stiching

There could be several reasons why the cotton is not being pulled from the bottom to the top. Here are some things you can try:

1. Check the bobbin: Make sure it is wound properly and inserted correctly in the bobbin case. The thread should be going in a counterclockwise direction.
2. Check the needle: Ensure that the needle is the correct size for the fabric you are using and is inserted correctly. A dull or bent needle can cause problems with thread tension.
3. Check the tension: Make sure the top and bottom thread tensions are correctly set. The thread should be able to move freely through the machine without being too loose or too tight.
4. Check the feed dogs: The feed dogs should be in the up position and moving the fabric smoothly through the machine. If they are not working properly, the fabric may not be moving through the machine correctly.

If none of these solutions work, there may be a mechanical issue with the machine that requires professional attention.

Can be several causes. In typical probable order for rotary hook machines;
1.Top thread tension is too high (lower tension)
2.Top thread snagging at spool or elsewhere (for hoizontal spool use larger spool cap and/or machine not threaded per specific instructions)
3.Bent needle or barbed needle point (replace needle)
4.Needle not properly inserted into holder (see specific machine instructions)
5.Debris in shuttle hook/race (clean bobbin, hook, race)
6.Wrong bobbin (replace with proper machine bobbin)
7.Bobbin thread tension too high (reduce bobbin spring pressure, likewise top thread tension)
8.Poor quality or extremely light thread (if using cotton only thread, test sew with a polyester blend and see if problem goes away)
9.Bobbin case (replace bobbin case)
10.Machine timing. (check/adjust timing)
11.Burr in hook race, this can happen if a broken needle point jams in the race (remove burr or replace race)
12.Machine timing. (adjust timing)
13.Hook is worn or damaged (typically not a worn hook unless a few hundred hours of use, look for a barbed or bent hook point) Watch following Singer video... see testing top thread tension.
https://www.youtube.com/watch?v=O7N4XaIV6ms
and following animation on generic rotary hook sewing https://www.youtube.com/watch?v=zqRvljnNLFk

check the age of the cotton
cotton is not a single thread but a series of fine threads bonded with a glue
old cotton glue breaks down and the thread separates easilty
next check that the needle is installed correctly with the grove ( thread groove away from the bobbin hook
check the needle and hook timing because if it is off a fraction , the hook will pierce the the thread causing it to break
next check that the eye is the correct size for the thread in use
a needle eye too small for the thread thickness will jam the thread ans not let slide through the eye properly

Install a brand new needle and confirm it is inserted with the flat side facing the proper direction.. A bent, damaged needle will sometimes cause skipped stitches or even needle strikes inside the machine. A new needle is the least expensive cure for a lot of sewing machine problems. The needle should be changed about every 8 hours of sewing or at least when starting a new project.

Remove the top thread. ALWAYS RAISE the presser foot and rethread from the beginning. Verify the thread path is correct.

Sometimes, skipped stitches will occur if the needle, thread, and fabric are incompatible. Be sure to use the correct needle for your project. Use a good quality thread--AVOID old or bargain bin thread!

If the machine continues to skip stitches, then it may be out of time. Search for sewing machine timing or take it for service.

Basic Maintenance Tension Skipped Stitches

What to Do If Your Sewing Machine Is Skipping Stitches

Don Ignore Your Sewing Machine Skipping Stitches Simple Solutions

You might try cleaning the tension disks by dampening a length of pearl cotton with rubbing alcohol, open the tension disk all the way, raise the presser foot, and then pull the pearl cotton down between the disks a couple of times.

Clean away the lint and thread pieces from the feed dogs and bobbin area. Oil your machine according to the instruction manual--use only fresh good quality sewing machine oil--only 1 or 2 drops of oil each place.

Install a brand new needle. Make sure you are using a needle and thread that are compatible with the fabric you are sewing--that the thread is not too big for the needle's eye, etc.
All About Needles

Make sure you RAISE the presser foot BEFORE threading the upper thread. Rethread the thread from the beginning checking that thread is not wrapping around the spool pin or catching somewhere in the threading sequence.

Verify that you are threading the machine correctly. Misthreading will cause havoc and frustration!

Do not use old or bargain bin thread--Coats & Clark does create problems for some machines.

You might try pulling the bobbin thread to the top before beginning to sew. This helps prevent some of the thread nests you are experiencing.
How and Why to Bring up the Bobbin Thread

The factory tension setting is usually the halfway point between the high and low number. This is where you should start testing your tension. Once you sew a sample, if the top thread is looping/knotting (bird nesting) under the fabric, the upper tension is most likely too loose. If the bobbin thread is pulling to the top of the fabric, the upper tension is too tight. Get used to adjusting the upper tension every time you change fabric, needle, thread. The upper tension is not meant to be static, so don't be afraid to adjust to achieve the proper tension.

Ideal tension is when both the upper thread and bobbin thread meet in the middle of the fabric.

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I have solved my tension problems by going to threadmagazine.com. they have solutions to many, many problems you have with your sewing machine. Hope this helps. jdokos95

Do you have thread in your bobbin?
Is your needle fully inserted in the needle bar?
Is it the right needle for the machine?
Is your needle damaged, bent or dull?

The key to proper stitches is that tension on the bobbin must equal the tension on the upper thread spool as well. The bobbin has a tension screw that may have come loose or the thread is not properly in the tensioner. For example, the bobbin could be in backwards. Or the tension of the top could be too light and allowing the tension on the bottom to pull the thread down too much.
Open the bobbin tray and watch while you slowly rotate the hand control to see it make a stitch.
You will probably be able to figure out what is wrong.

put a new needle in the machine
clean under the needle plate where the feed dogs are for lint
clean in the bobbin area for lint & loose threads
also rethread the machine, make sure you get every thread guide

This may be of help:

How to Thread Necchi Sewing Machine

Even though your machine is probably a different model, machines generally thread the same.

Something that may help is ALWAYS RAISE the presser foot when threading the top thread. This allows the thread to seat fully in the tension disk and helps eliminate those loose threads under the fabric.

If the bobbin thread still just lays on the fabric, the top tension is too loose. Tighten the top thread tension so it will pull the bobbin thread up into the fabric. Tension is a tug-of-war between the top and bobbin threads. Neither should win nor lose. Tension is accurate when both threads meet in the middle of the fabric. Also, keep in mind that tension is not static, ie it will most likely need to be adjusted whenever you begin a new project because the thread, fabric, needle, and stitch selection can change the tension.
http://www.threadsmagazine.com/2008/11/02/understanding-thread-tension

You shouldn't need a separate spool for the top thread if your machine has the vertical spool pin. Most spools will work unless you are trying to use the huge spools that are made for sergers. In that case, you can wind thread onto a bobbin and then use the loaded bobbin as your top thread--in effect, you would wind 2 bobbins, one for the bobbin thread and one for the top thread. If my thread spools are taller than the spool pin (causing the spool to flop around when I stitch), I simply slip a plastic drink straw over the spool pin and, Voila!, the spool pin is taller than the thread spool.

Another helpful hint: AVOID using old or bargain bin threads. Quality thread will limit a lot of sewing problems and frustration.

Install a brand new needle every 8 hours of sewing time. Frequently, problems are a result of using old, damaged, or dull needles. When having problems, the first course of action is replace the needle. A lot of time can be spent trying to find resolutions to a problem when a brand new needle is all that's needed. If you hear the needle strike something strange, it's probably best to replace the needle as it has probably been damaged or bent. A hard strike of the needle can knock the machine out of time which would require a visit to the service repairman.

Second step to problem resolution--rethread the machine. Remove the thread completely from the machine and start over from the beginning. Verify the thread path is correct.

Also, using the correct needle type and size for the project is important. Don't use needles whose eyes are either too small or too large for the thread. Use a needle made for the type of fabric and project. Use embroidery needles when embroidering, use ball point needles for knits, use sharps (universal, microtex...) for woven fabrics, leather needles for leather, denim needles for denim/heavy fabric, etc.
https://www.schmetzneedles.com/all-about-needles/

Last but NOT least, perform maintenance on your machine every 8 hours. Clean lint and loose threads from the bobbin area, the feed dogs, and under the needle plate. OIL (use good quality sewing machine oil) and apply just a drop or two every place according to the manual. Do NOT use 3-in-1 oil, cooking oil, motor oil, WD40 or any oil other than fresh, good quality sewing machine oil!

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