I bought a second hand babylock eclipse serger, the pproblem is the width sticth adjusment is stack, how do I slove it.

You mean 'stitch length'? Width would be governed by the needles width

Manuals

Page 5 - Part 24 = Stitch Length Dial

https://www.manualsdir.com/manuals/719470/singer-wsl2000-ats-part-1-wsl2000-ats.html


https://www.google.com/search?q=white+superlock+2000+ats+manual+pdf

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It sounds like you are having an issue with your Lervia 564 sewing machine. To reset the stitch width knob, you will need to follow these steps:

1. Turn off the sewing machine and unplug it from the power source.
2. Locate the stitch width knob on the machine. It is usually located on the front or side of the machine, near the needle area.
3. Grasp the knob and gently turn it counterclockwise to the left until it stops.
4. Plug the machine back in and turn it on.
5. Test the stitch width by selecting a stitch pattern on the machine and adjusting the width knob to see if it is working properly.

If you are still having difficulty with the stitch width knob after resetting it, you may need to refer to the machine's manual or contact the manufacturer for further assistance.

indicates a problem with the sew direction level /knob or control
if it is in neutral the dogs do not come up and the length of the stitch depends on the dog movement

Hello Jo C:
Instructions on moving seam width finger knob are on page 57 of your manual (available at http://www.singerco.com/uploads/download/555_14sh644_654-(e_s_f)-(new-led-version).pdf if you need one).
Also make sure that the blade is to ful left as this makes moving the stitch finger easier.

Happy Stitching
Sewingirl/

A transcript from the Elna SU manual reads as follows, and the manual can be viewed on line at http://sewingonline.co.uk/instructions/elnasp/

First make a few trial runs with a scrap of material exactly as the buttonhole will be stitched, with the machine adjusted as you intend to use it.
1. Use the embroidery and buttonhole foot. It can be chnged without a screwdriver by using the fixation screw.- With the stitch width knob at "0", turn the selector to zigzag "1".
2. De-center the needle to the left.
3. Set the stitch width knob at 2, with the solid mark on top.
4. Set the stitch length dial between 1/2 and 1/4.
5. a) Mark the desired length on the material.
b) Sew the first side of the buttonhole. Stop with the needle in the material and the mark (right).
c) Raise the foot and pivot the material round the needle. Lower the foot and raise the needle.
6. a) Set the stitch width knob at 4.
b) Sew a few stitches. Raise the needle.
7. a) Set the stitch width knob at 2.
b) Sew the second side and stop just short of the length of the first. Raise the needle.
8. a) Set the stitch width knob at 4.
b) Finish off the buttonhole by sewing a few stitches. Raise the needle.
9. a) Set the stitch width knob at "0".
b) Sew a few stitches to fasten the threads, holding the material back by hand.
10. Open with the buttonhole knife, which you will find in the accessory box.

Hello

The stitch dial for the length is located all the way on the right side of the machine and is factory set at the setting "3," which is a 3mm or 1/8 inch length. Turn the dial up or down to adjust the length. For example, the setting "4" is 4mm (5/32 inch) and "2" is 2mm (5/64 inch).

The width of the serged seam is dependent on the needle or by adjusting the knob for the width. With the left needle only sewing, the width is set to 7/32 inch, and with the right needle only sewing, it is set to 9/64 inches. Additionally, by pushing in the width adjustment knob behind the front cover, the stitching can be adjusted manually from 1/8 inch to 17/64 inch wide.

You move the top blade to the right to trim less so stitch forms wider and use left needle. Or both needles for 4thread seam which is more for knits. Blade has a knob usually to adjust it's position. You should test on scraps of your fabric as the weight of the fabric will also determine width of the seam. Adjust top and bottom looper tensions to encase cut edge neatly.

Here is the info about this serger from the baby lock's website. It says the stitch length is a dial. I couldn't find the manual for download, but they say they stand behind their products with support. I would follow the customer support link at the bottom of the page and request a user manual. It looks like they sell an instuctional video and optional workbook too. Might be worth the price to help you get the most out of your seger. Hope this helps!

http://www.babylock.com/sergers/previous-models/eclipse-lx/

There are 3 things that come to mind for me.  I should say that I have a Bernina 1300DC, so your machine may not have the same parts, but check these things.  First, are you using 3 threads?  If so, is your needle in the narrowest setting, in the right hand hole closest to the body of the serger? Secondly, is your rolled edge lever retracted?  This lever is attached to a wide tooth that holds the width of the seam in place.  It is under the presser foot, between the loopers, and should retracted so that the stitches are allowed to become narrow.  If your machine doesn't have this lever, don't worry, you can also try a third thing.  Adjust your cutting width to a narrow setting.  There should be a knob that moves the upper cutting knife from right to left-- right being a wider seam, leaving more of the fabric intact, and left making a narrower seam that trims off more of the fabric as you sew. 
Hope this helps! Elsje

The factory settings are 4, 4, 4, 4, and width at M. Hope this helps.