Thread breaks right away and is all bunched up on the bottom stitch

Check your stitch sample. The loose stitches under the fabric--are they actually top thread???? Usually,stitch problems under the fabric is a result of a top thread problem. In this case, it could be bird nesting.

Remove the top thread from the machine.
Install a brand new needle.
ALWAYS RAISE the presser foot.
Rethread from the beginning.

Sewing Machine Thread Bunching Up Here Why

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

Skipping stitches and thread breaks
Skipping stitches and thread breaks

Sewing Machine Thread Bunching Up? Here's Why!
Sewing Machine Thread Bunching Up Here Why

Are you 100% sure you are using the right size bobbin?

It sounds like you have no tension on the bottom bobbin reel. Did you check your tension on the bobbin reel. The tension must be right on both sides. When pulling on the cotton when the reel is in its bobbin case you need to feel a little resistance. Adjust the tiny srew on the bobbin case to tighten the reel to avoid it to turn in the casing.

You need a fatter needle. The skinny needle will not open the leather enough for a smooth flow of thread and that's why the bobbin is bunching up when the top thread is sticking. Make it easier on your machine by using an appropriate size needle while sewing leather.

whether its bias or straight does not matter to machine. loosen the bobbin tension and put more tension on take up spring by inserting a screwdriver in the slot of the top thread tensioner. turn to right.

try adjusting the top thread tension and see if that helps
also try changing the thread.
also change the needle--make sure it's the right needle for the fabric
being sewed.

Make sure you hold thread in back of the lowered presser foot when you begin stitching, and that the needle is piercing the fabric so that the fabric isn't slipping down into the feed dogs (under needle plate area).Hope this helps you out,alexlefebvre.Jimmy

I always adjust my overlocker stitch in several ways. I start test serging with the blade set right out to the right so that it "fills" the stitching. I'll set all the thread dials to the middle setting, ie. 5. Then I test serge, and check the stitch formation. If the needle is looping underneath, then I'll tighten it "A LITTLE". If the looper threads are lying off the cut edge of the fabric, then I'll dial both the top and bottom looper numbers up a little to make those threads tighter.

Each fabric behaves differently depending on its "hand" so the right stitch settings do vary, ie. organza is different to heavy weight cotton or denim. So if my inital setting is then "bunching" up the fabric within the stitching, I will then lower the numbers for the top and bottom looper to release the thread some. And if the fabric is very soft and light and still bunches up, then I will move the blade over to the left some, cutting a narrower edge within the overlocking so the threads lie better.

So revist the settings, check that the cones are flowing freely, thread is into the tension devices fully, then retest the stitching. If it is the top looper only that is looping off the edge, and not the bottom as well, and they are both set to the same number, then I'd be a bit suss about the tension dial.

Could be a tension issue.

Try this to see if it helps:
Remove top thread.
ALWAYS RAISE the presser foot and rethread from the beginning.
Start the top tension set at the midway point and then adjust.
Check that the bobbin is threaded and installed correctly.

Understanding Thread Tension Threads

Sewing Lesson 10 How to Fix Tension on Your Sewing Machine