Top thread will not pick up bobbin thread makes a big loopy mess

Re-check your stitch sample. Pull on the loopy thread. Is it really the bobbin thread, or is it the top thread looping under the fabric? FWIW, stitch problems appearing under the fabric are usually top thread issues, stitch problems on top of the fabric are usually bobbin related.

You can try this on both of your machines to see if it makes a difference.

Be sure to install a brand new needle.
Remove the top thread completely from the machine.
ALWAYS RAISE the presser foot and rethread from the beginning.
Make sure the thread path is correct.
Set the top tension to the midway point and retest your machine.

If the top thread is showing under the fabric, tighten the top tension, If the bobbin thread is showing on the top of the fabric, loosen your top tension. The perfect tension is when the two threads meet in the middle of the fabric.

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Hm, if the bobbin thread stitch is inconsistent, I would guess it is a problem with the bobbin tension. You might try picking up a new bobbin case for our machine. Bobbin cases do wear out or get damaged or there may even be a burr somewhere that is catching the bobbin thread.

Something else to try, before buying a new bobbin case, is:

Avoid old or bargain bin threads!
Install a brand new needle (compatible with the fabric & thread).
Remove the top thread from the machine.
Try a different brand of thread.
ALWAYS RAISE the presser foot and rethread from the beginning.
Set the upper tension to the midway point and test your machine.
Adjust the upper tension until the bobbin and top threads meet in the middle of the fabric.

try a new needle

try adjusting the top thread tension to see if that helps the bottom loopy stitch

1)Check that your bobbin does not have a nick in it where the thread can catch and won't feed smoothly.2) make sure the upper and bobbin threads are the same.3) pull out the bobbin case and chect to see if there is a clump of lint.4) make sure the feed dogs are moving the fabric through smoothly,some fabrics can get caught on the dogs and make the bottom thread get loopy.5) check your needle,if it's bent or has a bad tip,it can mess up the stitch.

Check your top tension. It sounds like it may be too loose or the bobbin tension may be way too tight. Most likely it is the top tension that is incorrect though. The TOP tension effects the bottom side of the stitch and the bottom tension effects the top. If the top tension isn't tight enough it won't draw the thread up through the top side taunt enough and the excess underneath makes a big loopy mess.

Recheck the tension on the top thread. Test it before you put it through the needle to see if there's any tension. It should pull but with some resistance. Also check the needle and make sure it is the right type for the fabric and not bent etc.

Looping on the underside of the stitch is from the upper thread, usually tension problem. But do check the bobbin tension and make sure it isn't too tight, though that's not usually the problem you're describing. The two tensions need to work together in order to get a nice, flat (not puckered or loopy) stitch.

One last thing you might check too, though again this wouldn't typically be the problem - is the dogfeed moving the material along under the presser foot correctly?

Most of the time the problem you're describing is due to not enough tension on the upper thread.

If the bottom stitching is a mess it usually means that the TOP thread is not threaded correctly. What happens most of the time is that the thread is not snug in the tension discs. First re-thread your machine with the presser foot UP and when you get to the tension discs (sticking up at the back of the machine) hold your thread like you're flossing and go back and forth in the disc to make sure you have tension on it. You should hear a little click when it's in there. (Test it...floss it on and pull it off so you can hear the click.) If the thread isn't between these discs your bobbin thread will be loopy. Finish threading the machine and you should have no problem now. Also, make sure your upper tension is set at 4 and your stitch LENGTH (on the right front) should be 2.5 or 3 for a normal stitch. Hope this helps. Let me know! Thanks for using FixYa

Usually if your bobbin thread is loopy it's because the TOP thread is not threaded right. Try threading it again with the presser foot UP and make sure to get the thread between the upper tension discs. It's just the opposite of what you would think.....if the bobbin thread is loopy, the top thread is threaded wrong, if the top thread is loopy, the bobbin is threaded wrong. Good luck!

loopy mess = upper tension/threading is wrong

This could either be due to the bobbin being wound too loosely, or the tension on the top thread is too loose. This just happened to me the other day, and I thought it was the bobbin thread, but then I put another bobbin in with a different color than the top thread (this is a huge help in diagnosing thread issues), and I was surprised to find that it was actually the top thread that was a big loopy mess on the underside of the fabric. I fixed it by tightening the tension on the top thread (quite a bit), and everything was fine.