The tension of thread is too loose on the underside when sewing decorative stitches

It is a tension problem, check your needle to make sure it does not have a burr this will cause thread to break.
if the stitching is loose on the underside you have to figure out if it is the top thread going to the underside and making loops of thread, your tension is too loose so tighten ever so slightly and sew a few stitches till it is even, if it is the bobbin thread that is bunching up try re threading it and make sure you are using the same thread on both bobbin and top, some will not work together. hope this helps good luck

When the underside of the stitching is loose the problem is most likely with the top thread. Unthread the machine then rethread it making sure that the thread is securely in the tension disk and the machine is correctly threaded.

According to the manual, you should not need to adjust the bobbin tension (and I located other sites which stated the bobbin tension cannot be adjusted on this machine). Apparently, all the tension adjustment is accomplished through the upper thread::
"EN Thread Tension Upper thread tension Basic thread tension setting: "4". (1) To increase the tension, turn the dial to the next number up. To reduce the tension, turn the dial to the next number down. A. Normal thread tension for straight stitch sewing. B. Thread tension too loose for straight stitch sewing. Turn dial to higher number. C. Thread tension too tight for straight stitch sewing. Turn dial to lower number. D. Normal thread tension for zig zag and decorative sewing. Correct thread tension is when a small amount of the upper thread appears on the bottom side of fabric. Lower thread tension The bobbin tension has been set correctly at the factory, so you do not need to adjust it. Please note: - Proper tension setting is important for strong seams. - There is no single tension setting appropriate for all stitch functions, thread or fabric. - A balanced tension (identical stitches both top and bottom) is usually only desirable for straight stitch construction sewing. - 90% of all sewing will be between "3" and "5". - For zig zag and decorative sewing stitch functions, thread tension should generally be less than for straight stitch sewing. - For all decorative sewing you will always obtain a nicer stitch and less fabric puckering when the upper thread appears on the bottom side of your fabric. 1 A B C 22 D"

Doing further research, I found this statement on a machine review site:
"After reading reviews online from where I've bought my drop-in bobbin machines, I think many of the negative reviews are due to the bobbin thread coming up without laying across the bobbin. It can cause the stitches to look very sloppy and no amount of tension adjusting can fix the stitches."

There are several machine review sites wherein 4423 owners stated their disappointment in the 4423's performance. Some said the machine failed almost immediately and others said the machines developed problems when sewing heavy fabric.

Firstly check the tension on your bobbin case is sufficient or if the thread is actually into the spring fully, this is most likely cause of bottom thread loose stitching. You can test bobbin case tension adjustment using the "Dangle" test, here is a link to some good images to help.
http://www.sewusa.com/Sewing_Machine_Repair/Thread_Tension_Settings.htm

If you look closely and there is actually looping on the underside then is is the top thread coming to the underside and not being tensioned back up; so top thread is not under tension enough or at all.

Set top tension to 4-5, then recheck the threading up and and always thread with the presser foot raised as this opens up the tension device so the thread can seat in fully. Once you've threaded to just before the needle thread guide, lower the presser foot and pull the thread downwards, it should be very firm if its under tension.

Tension devices can get gunked up or fail with use so if you can't get it to feel firm, it will need a technican to investigate further.

Usually thread too loose on the bottom is caused by the upper tension being too loose. The top and bottom tensions work together with the top thread making the underside of the stitch seem too taunt or too loose and the bobbin thread causing the top side of the stitch to be loopy or too tight. Select a large zig zag stick and sew a couple of inches. Then examine the stitch. It should look identical on both sides. Look to see which side is drawn too tight, the zig zag being smaller on that side with threads from the bottom threads pulled through. Then adjust the two tensions so that they make a uniform, identical stitch.

Also, when the bobbin tension is right you can hold the bobbin dangling by the thread and it won't spool out to the floor but will let loose a bit with a slight flick of the wrist. Too loose it will just spool out. Too tight and it won't drop at all. When you get that set right then do the above zig zag test to see where the top tension should be set.

A. To correct loose stitches, try the following: (1) Balance the thread tension. If the stitches are loose on top of the fabric, decrease the tension to the next lower number. If they are loose on the underside set the tension to the next higher number. (2) Make sure the needle/upper thread follows the threading path. (3) Check to see that the bobbin case is threaded properly. (4) Use a different size needle. For fine fabrics, use a smaller needle (size 9, 11); medium-weight fabrics require a size 14 or 16. And use a size 18 or "Denim" needle for heavy corduroy or denim.

Hi Lou! This sounds like a tension problem--the tension on the top thread is too loose. Try using different color threads on the top and bobbin, then carefully rethread everything. Stitch a couple of inches and check the underside. If the top stitches look fine and the bottom ones are loose and loopy, and with the pressure foot down, tighten the tension. Move the knob or dial (whichever you have) just a little bit. Sew a couple of inches more, and recheck. Continue to sew and recheck, gradually tightening the tension, until you see little if any bobbin thread on the top or top thread on the underside of the fabric.

Let me know if this helps, ok?


Robbie

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

It's very possible the bobbin is in upside down and the thread is coming out of the lower tension. Pull on the thread and the bobbin should turn counter clockwise if it is correct . If it turns clockwise, flip the bobbin over , put the thread through the lower tension and try it again. The topside stitch is loose either because the lower tension is loose(or non-existent) or the top thread is too tight.
sewman7

If the top stitch is loose, then you need to tighten the bobbin tension: if the bottom stitch is loose, tighten the top tension. Hope this helps. It could also be the size needle and thread you are using for a particular fabric. Different fabrics require different notions.