This image should Fixya !!
Also scroll down further to see a guide to tension setting.
Please TRY the solution BEFORE giving your considered rating.
Ensure that all is clean and free of lint and jams, this is the most likely cause....now for tension troubleshooting .......
Thissolution is for tension problems...if you cannot form any sort ofstitch, the issue is quite different, so please let me know if you needa different problem solved.....
It is quite long, but just work through each section in order.
The"knotting up" can reveal a lot. If you have loose threads on one sideor the other, the tension on the opposite side will be the culprit.
QUICK SUMMARY FIRST:
Ensure sharp new needle,
Thread guides and Bobbin are Clean & Clear of lint
Set Top Tesion to 4 ....then....
Balance Bobbin to suit.
TOP THREAD TENSION:
Ifthe looping threads are on the underside as you sew, it is the toptension. Top tension ought to be between 4 & 6 (this variation toallow for the different weights of fabric in your
IS YOUR NEEDLE SHARP ?
If you are using a needle that has seen quite a deal of work, or you suspect it may be blunt, change it for a new one !
TOP TENSION & GUIDES:
Makesure that when you thread the machine the presser foot is up so thethread goes between the discs and not to one side, top tension between4 and 6, and that you have threaded through all the guides, includingthe last one, usually on the needle arm, just above the needle clamp.
Itmay be there is lint trapped between the discs, this will keep themslightly apart and reduce the actual tension, sometimes dramatically.
Iftensions appear correct, and the thread is definitely in the channelbetween the discs, but still too loose and looping, try raising presserfoot and remove your thread.
Now, with a 2" (50mm) wide strippiece of fabric 8 - 10" (20 - 25cm) moistened with methylated ordenatured spirit, gently insert the fabric strip and clean between thediscs with
a see saw / to and fro action.
In the worstcases, gentle use of a needle to pick & remove the jam may benecessary, but be very gentle and make sure the tension is set at Zeroand the presser foot is raised, (to
disengage tension plates).... do not gouge or score the plates, they need a polished surface to work correctly.
Farless common, but if the loose threads are on the top, it is bobbintension that is loose, it too may have lint in the spring and be givinga "false" tension.
I would not recommend fiddling with bobbintension without good reason, it may end up with missing small screwsand spring pieces, however, you can take the needle plate off to clean
the hook race area (where bobbin case sits)
...this is just good housekeeping, my wife does this every time she replaces the bobbin....
justtake it out and clean the bobbin case and the fixed metal hook racewith a small brush to remove lint. If there is a significant amount oflint, use a vacuum and small brush to get the worst.
Then wipeall this area with a cloth or cotton bud (Q tip) moistened (not soaked)with methylated spirit, especially if there appears to be fine dirtydeposits....oil and lint combine to conspire against you.
If itseems likely that you ......really ....do .....actually .....need.....to adjust the bobbin case, first check there is no lint trapped inthe metal spring where the thread is tensioned.
Drop-in Bobbin case will look similar to this image with the tension screw in the middle of the metalwork....
...the other screw at one end is holding it all together, sobeware....it is not a tragedy to undo the whole lot and clean it, butvery gingerly and lay the bits out in sequence and orientation, or yourisk tearing your hair out !
....this is abobbin case from a front loading machine and works in a very similarfashion to the top loader with drop in bobbin, again, if you dismantleit, take care so you can put it all
GETTING THE BALANCE RIGHT:
Whenyou are certain there's no trapped lint in top tension or bobbin, setthe top tension to 4 and the bobbin tension to a point where you justbegin to feel resistance.
Try using good quality thread of contrasting colours so you can more easily spot the changes.
Setyour zigzag to one width less than maximum (eg. 5 of 6 ...or... 4 of 5etc) and sew a sample for a few inches and check the result.... adjustthe bobbin tension screw very little at
a time, perhaps 1/16 of a turn.
Youmay find you are playing with this balance for some little while and ifyou are putting the needleplate on and off each time begin to think itcannot be correct to do this.....BUT....it is,
and eventually, youdo get a "feel" for the correct tension and then it happens quitequickly.....as a user you won't be doing it very often unless there islint built up (or are there small hands at work around the house !?!?!)
Ifyou live near the ocean as we do, salt air can play havoc withmetalwork inside and out, so to help minimise this, keep a few smallpackets of dessicant (silica gel) in your machine
case....no case ? then make some sort of cover !
Same applies in any damp or humid environment, keep your machine dry and dust free.
Budgetfor a proper full service every couple of years (more often if heavilyused) and if you don't use your machine for a few years, be aware thatold oil will dry out and combining with
dust and form a "clag" like glue (another reason for some sort of cover, even a teatowel !)
FINALLY, A WORD ON THREAD:
Ifit is worth spending the time, energy and money on making somethingthat you would like to give lasting enjoyment......use quality thread,.......it may seem to cost a little more at the
time, but theresults, ease of use and added longevity will be worth the extra, andas a bonus, your tension troubles may be fewer and further between,because there is a more consistent diameter with good thread, and lesscompensating to be done by your tension plates and less thread breaks !bargainbox.com.au