I have checked the tension (hopefully I know what I am doing). My machine is a Brother XL-3500i. This is the most frustrating part of sewing is when that dang machine messes up.

Try a new needle!!

CLumping may be a sign of a dirty hook or bobbin area. Good idea to clean it all out, oil the hook, rethread everything, and start on a sample piece incase you have any extra oil. Good luck.

Usually, when this happens to me it turns out to be an upper thread issue, not a bobbin issue. Especially given all the attention you have given the underside of your machine. Try putting contrasting thread top and bottom. Change your needle, make sure there isn't a piece of thread or lint stuck in the tension discs, rethread the machine and try again. Good luck! I hate tension issues, they are one of the most frustrating things.

I own various vintage sewing machines, mostly Singer's, but each machine is different. Since this problem seems to be rampant only in Michigan I don't know if a Wisconsinite with Singer experience can help ( :) ) but here goes.

(These are some tips I wrote our for our married son when I gave him a sewing machine recently.)

1. Thread path: Make sure your tension disk's are clear. Use a length of unwaxed dental floss and 'floss' out between the disks when the presser foot is in the 'up' position.

2. When threading your machine, make sure the presser foot is in the "up" position. While in the 'up' position your tension disks are released and you can get the thread in the disks properly.

3. Consult your manual, make sure you are threading correctly and that your thread is staying in ALL guides.

4. Needle: Make sure the flat side of your needle is inserted in the proper direction. Consult your manual for proper direction.

5. Needle: Replace your needle. The slightest burr or wear or bluntness on your needle can cause headaches.

6. Look inside your bobbin case with a strong flashlight.
a. Do you see dust bunnies? Clean them out - DO NOT use compressed air to blow out dust bunnies.
b. Do you see pieces of thread stuck in there? Clean them out.

7. Re-wind your bobbin. Do NOT wind a new color thread on top of an old color. More problems are caused by this than you would realize.

8. Put your bobbin back in the bobbin carrier. Did you put the bobbin in the carrier correctly? Should the bobbin thread be unwinding clockwise or counterclock wise? Check your manual to verify which direction is correct.

9. Pull your bobbin thread through the bobbin spring so the thread is exiting the bobbin carrier correctly and put the bobbin in place.

10. Holding the tail of the upper thread, lower your needle enough to bring up the bobbin thread. Slide the bobbin plate closed.

11. Pair up upper and lower threads until you have about a 2" tail of thread.

12. Position your material.

13. Lower the presser foot.

14. Commence sewing BUT hold on to the 2" thread tails until you have a few stitches in your material.

Mom3 said most of this while I was posting mine...My experience, and the training I've received, says that normally if the thread problem is visible on the bottom of the fabric, it's a problem with the top tension and if the thread problem shows on the top, it's a bottom tension problem. Most common correction is to simply rethread the top thread. It could be that there is lint in the tension discs which throws the tension off, the thread has slipped off the "track", etc. There's a dental floss that has a lot of texture in it...made for dentures, I think, and it provides some extra texture to help clean the discs, just run a length of it through the top thread track and run it back and forth a few times to clean the discs.

Mine was doing the same thing......it was the top spool of thread. Somehow it got twisted around the little pole it sits on and wasn't/could't distribute the thread evenly. Check you top spool to make sure.

I had this same exact issue yesterday. I took the bobbin out twice and still had the problem. I then decided I would rethread the needle a lo and behold the thread had jumped out of the uptake lever! Rethreaded the machine and I was back in business!!!

Personally, I think it's interesting when the thread does a 'lasso' around the needle. Hard to see but sure screws up sewing.

Sounds like you've gotten plenty of suggestions and the ones I had were all taken. But I wanted to let you know that I feel your pain I've had this issue several times and it seems theres a variety of things that can cause it. Good luck!