I HAVE A BROTHER LS-2125 SEWING MACHINE AND THE STITCHING UNDERNEATH IS OK BUT THE UPPER THREAD IS LOOSE AND ALSO SKIPS

hi Sharon.
not sure if this will help you out because its saying its for the, ls 2125i.. but try this step by step link.


How to Thread Brother Ls 2125i Sewing Machine
or this youtube video link.

How To Thread Bobbin on Brother LS 2125 Sewing Machine

this link might be the best one for you to watch.when you go to this one scroll down the page a bit and you will see where you can watch the video,
How to Thread bobbin on the Brother LS 2125 sewing machine

Without more description of the stitch symptoms, the only suggestion is that the tension is too loose. Whether it is the upper, bobbin, or both tensions, we cannot answer without more information.

Understanding Thread Tension Threads

Sewing Lesson 10 How to Fix Tension on Your Sewing Machine

..

check to see if the top thread is coming off the thread take up lever
also try changing the needle
clean under the needle plate & bobbin area for lint or loose threads

1. Tension
   • Your sewing machine tension controls the rate at which the thread is fed through either the upper section of your machine or through the bobbin case. If your upper or bobbin threads aren't threading properly, sometimes adjusting the tension will correct this problem.
     
   Timing
   • Your sewing machine works by passing the upper thread through the needle of the sewing machine at precisely the same time the bobbin brings its thread to its uppermost position. If either the needle or the bobbin thread reach these positions too soon or too late, the threads won't interact and create the knots that make the seam. You can throw off your timing by sewing too many layers of fabric or hitting a pin with your needle. See you sewing machine repair facility to correct any timing issues.
     
   Thread
   • Thread can get snagged or caught in the upper section of your machine or on lint pieces in the lower bobbin section. If your threads aren't catching properly, you may be able to fix it by unthreading and rethreading both your upper thread and bobbin threads.
     

There may be a broken thread in the bobbin case effecting the lower thread tension. clean all parts and determine if the upper thread or lower thread is breaking if cleaning does not help. double check your machine threading and bobbin installation direction.
http://www.mastersewusa.com : this site has many operator manuals if the above suggestion does not help.

If your bobbin is the correct one for your machine and it is wound tight, not loose and puffy, make sure the thread is going the right way when installed (over the top to the left and then placed flat in the bobbin case). Usually if the thread bunches underneath your fabric it means that the TOP thread is threaded incorrectly. Try re-threading the upper thread. Good luck!

Could the thread be catching on the thread spool?

See this from Brother - http://welcome.solutions.brother.com/BSC/public/eu/gb/en/faq/faqh/000000/000000/000006/faqh000006_000.html?reg=eu&lang=en&c=gb&prod=hf_js23euk&page=FaqEndPage

The loopy stitching is usually do to threading the machine with the presser foot down.

Raise the presser foot and re-thread or pull about 8" of thread through the needle and see if the loopy stitches go away.

This may also be the issue with the zig-zag stitch.

When the machine is threaded with the presser foot down, the tension is closed and the thread cannot enter as it should for the tension to control the flow of thread to the needle. The thread then feeds too fast and the stitching is distorted.

Remove the thread from the machine.
Raise the presser foot.
Turn the handwheel until the take-up lever is at it's highest position.
Set the upper tension to 5.
Re-thread the machine.

loops on underside of fabric means upper tension or threading is wrong