It only takes a snippet of a thread stuck between the bobbin case and the bottom of the feeder feet to create this mess. I had this happen a couple nights ago. I had been sewing all day and late into the evening- no problems. Took a break to get a bite 10 minutes after I got busy again it started nesting after cleaning -re-threading top and bottom -changing needle -putting in new spool and bobbin I shut down for the night. The next morning I went in and took out the bobbin assembly I use a gun cleaning kit to get into all those tight areas and out came a piece of thread no bigger than this ''t'' Put the bobbin case assembly back in -and I was off and running smooth as silk.

Have not gotten back into my sewing room to try out hints yet. Hope to do so before DGS comes over after he gets off school bus.
Hope I don't have to take the tension assembly apart. Know I need to learn how to do so but right now is not when I want to. Lol!

If the machine was already sewing just fine I doubt if you need to take apart the tension unless you already had it apart.

Cleaned more thoroughly and it helped some but still not right. So took throat plate off and discovered even more guck.

Think I'm back to nice stitches now. And didn't have to take the tension assembly apart. Yea!

Thanks to all for the helpful hints and links to even more great info!

I'm glad you won one!

Stitch quality is still not quite what I want but ever so much better.

What kind of thread are you using? Thread really does make a difference. When the thread is nesting on the bottom, there's usually a problem with the top thread. Sometimes it may seem to be in the tension, but it's not. Or the tension dial has been knocked down to 0. I hope you're able to figure it out.

Caroline sent you a link to really good info for taking that tension apart and adjusting it. She has lots of info and some videos. Tammi is the best!

You might have a small thread caught in the hook assembly behind the bobbin. You can take off the hook assembly but don't lose the "gib" screw as the are not made anymore and it is very delicate. There is a tutorial on you tube which walks you through taking apart the hook assembly. I ended up going to a machine repair because I had stripped the gib screw.