Why does my Janome mb4 keeps shredding its top thread?

1. Check the thread: Make sure you are using a good quality thread that is appropriate for the type of fabric you are sewing. Poor quality thread or thread that is not suitable for the fabric can cause shredding and breaking.
2. Check the needle: Make sure you are using the correct size and type of needle for the fabric you are sewing. A bent or damaged needle can also cause thread shredding and breaking.
3. Check the tension: Check the upper thread tension to make sure it is set correctly for the type of fabric you are sewing. If the tension is too tight, it can cause the thread to shred or break.
4. Check the threading: Make sure the upper thread is threaded correctly and that there are no tangles or knots in the thread path.
5. Check the presser foot: Make sure the presser foot is properly installed and that the fabric is being held firmly in place while you sew.
6. Check the machine settings: Double-check that the machine is set to the correct stitch length, stitch width, and other settings for the type of fabric you are sewing.

If you have tried these steps and are still experiencing issues, you may want to consult with the technician who serviced your machine

I`m confused whether you mean top bobbin or lower bobbin...You can go back to the point where it broke...Brother machines are far more simple when this happens...

This is a tension issue with the top thread and also the bobbin. There should be adjustments for it on both parts.

Hello, Jerry -

I doubt the kind of thread and pre-wound bobbins you use with your Janome MB4 sewing machine are the problem with the thread tangles and loops on the bottom and top of the items you are working on are the problem. Robinson Anton threads appear to be rated as high quality.

I suspect the problems are caused by the tensions for the top and bottom threads and / or how the bobbin is inserted in the bobbin holder. It is an embroidery sewing machine, is it not?

From the user manual for your model of machine:
https://www.janome.com/siteassets/support/manuals/embroidery-models/inst-book-mb-4en.pdf
on Page 81 (PDF image 84), the problem of the thread looping (last Troubleshooting issue on the page) may be caused by
- Needle thread tension too loose
- Bobbin not inserted properly
- Poor quality thread used (Note: I don't think that is the issue for you.)

I found a series of YouTube videos about the Janome MB4 machine, which may prove instructive. This is the link to the Part 1 video:
https://www.youtube.com/watch?v=8VL-ikUr3tQ
In the right sidebar of that page, you will see links to the first parts of the video series. As you choose subsequent parts of the video series, you will see additional links to other parts of the video series in the right sidebar.

I also found a longer video tutorial on YouTube for the Janome MB4:
https://www.youtube.com/watch?v=X_RJ8-kY5_o
The sections of the video on inserting the bobbin (starting at about minute 14:18) and threading the machine (starting at about minute 15:17) may be helpful.

If, after making sure you know how to insert the bobbin properly in the machine and after threading the machine properly and setting the tension for each needle, you still experience thread nesting, I suggest you locate a nearby authorized Janome sewing machine service center and pay to have the machine evaluated and adjusted so that it works properly.

Best wishes.

The needle could be bent or have a burr--try putting in a brand-new needle that is compatible with the thread size and the fabric you are sewing.You could be using old thread that has deteriorated. Also, bargain bin thread is not the best quality to use. The thread may be too big for the needle's eye. The upper tension may be too tight. Also, RAISE the presser foot BEFORE threading the upper thread since this releases the thread tensioner and allows the thread to seat properly.

This guide may be helpful:
Sewing Needle Troubleshooting Guide

also other helpful information:
All About Needles

....

You may have already got it fixed or just don't use needle #1. If you have hit a hoop it will cause this. Take the front cover and top off the machine. At the top of the 4 needle bars there is a screw. Look to see if the screw on needle #1 is lower than the rest. You should be able to compare with the other 3 needle bars. Loosen this screw and slide it back up even with the others. This lets the needle bar go lower and hopefully this will fix your problem.

are you using a good thread and the same thread on the top and in the bobbin, different threads will sometimes act up. I also can not sew one brand of thread on my machine, try Mettler or gutermann's you can get them at JoAnn's or Fabricland. hope it helps good luck K

checks that the strip wire and strip wire sensor, this worked well.
(the strip threads is the small spring by which you spend the thread to thread)

check for burrs on the needle plate and in the bobbin area
also check for burrs in the threading area,like one of the thread guides

Hi!
I was having the same problem(s) and I loosened the tension on the bobbin case and switched to prewound paper bobbins and everything sews beautifully.
Hope that helps!
-Donna Jo