BeautifulBunting

This has been happening today only (that I've noticed).
I have changed the needle, re threaded top threaded, re threaded bobbin.
Any suggestions?
This is the back side of the material.

BeautifulBunting

Sorry I should say, the white is a bobbin thread, the green is a universal thread.
Also as you can guess by the question I'm pretty new to sewing

leatheflea

Well to me it looks like you've been making adjustments in each row of stitches. And you almost had the problem fixed in the third row from the left. Tightening your top tension might help if the the white thread is your top thread.

leatheflea

Sometimes if your pushing your fabric through this can happen. Okay the white is the bobbin, that means you need to loosen the top tension.

PaperPrincess

When you sew, you are looking to get the same amount of top thread on the top and bobbin thread on the bobbin. The zig zag stich has a lot of top thread so you are going to have a lot of bobbin thread showing. this is normal. What you want is a smooth stitch on the front and no bobbin thread showing on the front. You also want the stitches to lay flat and smooth. You don't want the tension so tight that it pulls the fabric together. Most embroidery units, which often use a zigzag type stitch tell you to aim for about 30% top thread to show on the back. I personally think that all your samples have the top tension too high. There's NOT ENOUGH bobbin thread showing and the fabric looks like it's slightly pulled. In the end, however, adjust your tension so the front looks good!

Tartan

If the white thread is the bobbin thread, then it looks like too much of the green top thread is being pulled to the back. Ideally you want the green thread showing on the top and only white thread showing on the back. If you can manage to get them perfectly balanced for your zig zag, you are a genius. I usually match bottom and top thread for this reason.
You can get a more balanced stitch by either tightening the thread tension on top or loosening the bobbin tension. Try setting the top tension back to the factory setting and look at your stitch. Tighten a little at a time and try samples. If that doesn't fix the problem, you may need to adjust the tiny screw on your bobbin case. Before touching the bobbin case screw, take a picture of it's position so you can return it to the original position if it doesn't help. The tiny screw on my machine goes tighty righty and lefty loosey. Make sure to adjust the screw over a bowl so you don't loose it. Good luck.

Holice

You don't say you have adjusted the tension only changed thread and bobbin.

BeautifulBunting

The 4 images are the 4 different tensions I used.

Quilter qld

It is a tension issue. Try what Tartan has said and see what happens. Next step match the colours top and bottom. Have you given your machine a clean recently. You may need to see a repair man. Happy sewing

nhweaver

Sometimes this happens to me when the threads are different manufacturers. I would suggest trying the same brand same weight thread, top and bottom (use different colors) to see if this helps the tension. What brand machine? computerized?