Pulling on top thread bunches my fabric

Your tension must be wrong. If the top tension is too weak the thread on the bottom is not being pulled through the fabric to form a proper stitch. Try different tensions on scraps of fabric.

Generally, bobbin tension is set at the factory and is usually a "last attempt" to alter. Sounds like you are probably experiencing bird nesting or thread nesting which is a top thread issue.

Be sure to install a brand new needle.
Remove the top thread from the machine.
ALWAYS RAISE the presser foot and rethread the top thread.
Set the top tension to the mid-point and retest your machine.

Tension is correct when top and bobbin threads meet in the middle of the fabric. It is a tug of war between the two threads. When there is equal pull, the top thread pulls the bobbin thread up and the bobbin thread pulls the top thread down. Increasing the top tension pulls the bobbin thread further up, decreasing top tension will allow the bobbin thread to pull the top thread down.

Understanding Thread Tension Threads

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Remove the top thread from your machine (NOTE: ALWAYS clip the thread next to the spool, lift the presser foot, and gently pull the top thread down from top to bottom!!! This helps reduce the chances of breaking something by pulling the thread upwards!)

ALWAYS RAISE the presser foot and rethread the top thread from beginning. Verify the thread path is correct and start out with the thread tension set at the midway point (and then tweak the top thread tension through testing).

FWIW, if the thread problem appears under the fabric, it is generally a top thread issue. If the thread problem appears on the top of the fabric, it is generally a bobbin thread issue.

What causes Bird Nests Superior Threads

Birds nest under the fabric big loops of thread top side looks good...

CURED Sewing Thread Nests on the bottom


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adjust the tension to a appropriate setting,
See the video here.
Sewing Help Sewing Machine Problem Thread Bunching Under Fabric
The knob and its location can differ based on the model of your sewing machine.

If you're getting the bunching of thread on the bottom of your fabric, make sure that you have the machine threaded properly on top. If you pull the thread through the needle with the foot up, you feel little or no resistance. If you put the foot down, the thread should become harder to pull and the needle will bow. If this doesn't happen, the upper tension is not working correctly or is too loose.

I had similar problems when I first started sewing. Try adjusting the tension in your thread - less tension for lighter fabrics, more tension for heavier fabrics. This will stop the needle from pulling the threads in the fabric.

As for the thread getting bunched up in the bobbin - this is most likely because your bobbin is the wrong size for the machine, or that you did not thread the bobbin properly. Try re-threading, this time making sure you pull the thread into the bobbin container tightly. This should stop the bobbin from jumping around the container and spitting thread.

Make sure that there is tension on the thread when you have passed it through the tension unit, by making sure the presser foot is down, and then gently pulling the thread to feel tension. If there is no tension, as seems to be the case, check the tension discs inside the unit to make sure that there is no debris stopping them from closing.

Take the thread off the top of your machine and rethread it. Anytime a sewing machine bunches up the thread on the bottom the cause is the top thread. Make sure the tension dial is on "5". After you thread the machine, put the pressure foot down,(like its resting on fabric, but not on the thread), and pull the thread towards the back of the machine. It should be somewhat tight. The needle should "bow" slightly before the thread comes through the needle.

The problem is never the bobbin when you have this problem. It's the top thread. Take the thread off the top of the machine and rethread the top. Make sure the small tension dial is on 4 or 5 (the larger dial on the front left is for the pressure on the foot, not the thread tension.) After you thread the machine, put the pressure foot down but NOT on the thread. Then pull gently toward the back of the machine. When you do, the needle should bend slightly backwards before the thread comes through the machine. If it pulls with no resistance you could simply have "fluff" or remants of thread between your tension discs. If you do, put the dial on zero and using an old needle, clean between the discs and try threading the machine again with the "pull test" I described earlier.
No tension on the top of the machine, lets the bobbin tension win and it pulls all the thread to the bottom of the fabric.