I've problem with my Necchi Lock 160 Overlocker. A needle broke and it was replaced. I got a chain stitch for awhile but now it won't chain stitch or sew. What should I do?

Replace the needle and retread the machine

try new needles
make sure tension is correct
could possibly be in need of some adjustment

You may need to override the current selection by selecting next design , then get back to your original design selection again. And this should work. However if still not working, just switch off your machine and after awhile put it on again. Hope this will help.

Did you thread in the proper order? Upper looper, lower looper, needles from right to left?

here's a link for a manual
http://www.sewingpartsonline.com/instruction-book-elna-t33.aspx
try changing the needles & see if that helps the machine to form
a proper stitch, if it doens't then it's possible that the machine
could be out of time & needs to be checked at a sewing machine
shop

is it possible that the needles are in backwards?
it's very possible that the machine is out of time & would have to be taken to a sewing machine repair shop to be retimed

for a manual try elna customer service
as for the needle, check to see if it's inserted correctly in the needle holder
the needle must be pushed all the way up into the needle holder--
the flat side goes to the back side of the machine
you also mentioned that you broke a needle, when a needle is broken some times it can cause the machine to go out of time, which means it has to be taken to a sewing machine repair shop & be retimed,,
and it needs to be serviced.

I can help you with your 334D as I have the same machine; there is several ways to adjust the stitching width but firstly check the stitching finger position is forward not back for rolled hemming. There is a little lever that is on the side of the cutting plate just in front of the foot and feed dogs, you need to push this forward; this inserts a stitching finger into the needle plate and the overlock seam forms around it. When you pull it back the finger retracts to form rolled hemming where you want the fabric to roll under. So hopefully this is all that is happening now with yours but I'll go through the whole process for clarity and others.

This is how I set up for a new fabric project. Turn the tension dials for all four threads to 5. Your needle tensions should not need to be changed often; perhaps just if from the right side of a seam you can see the needle stitch, you may tighten it fractionally. Stitch length knob on the side by the flywheel should be on about 2 and a half and the differential knob on zero also.

Now you want to adjust the cutting blade position firstly to get the width of seam best suited to the weight and type of fabric you are going to seam. If you are going to use the overlocker to join two pieces of fabric in a 4 thread seam to assemble a garment, then always test with two layers too. And if you are going to just neaten a single layer seam allowance, then test on just a single layer and set up for that.

I'm assuming you are seaming 4 thread but the comments are the same for the 3 thread, you just take out the left or right hand needle first or just cut the thread to that needle and leave it in place to get the 3 thread stitch. (Obviously if you are seaming something delicate like silk, take the unused needle out as it will leave holes in your fabric. Be careful when changing needles, use tweezers to hold the needle right up into the housing and never unscrew the screw too far, just enough to get the needles in and out. And always manually turn the flywheel towards you through a stitch sequence afterwards to make sure you've got the needles clearing the loopers, if you hear them touching, recheck needles are fully into housing.)

If you are seaming something light then you'll want a narrower seam. Have you moved your blade before? If not, you need to turn the needle to the highest point, open the front cover and raise the pressure foot and swing it to the side so you can see better. Now put pressure on the upper cutting blade towards the right to release the spring on it, then swing it upwards out of the cutting position. Adjust the position of the lower fixed blade by turning the knob that is nearby to it. You'll see the blade moving over. Once you get used to making this change, you can just put pressure onto the upper blade to release it with one hand, and turn the knob to move the bottom blade with the other.

If you move it towards the right it will trim further away from your needles giving you a wider seam and if you move towards the left you'll get a narrower seam, ie it cuts closer to the needles. So set it to the position you want depending on what you are seaming. Now relower the upper blade into position, swing pressure foot back into place and test stitch again on fabric offcuts. Take a look at the seam. Is the fabric "tunnelling" inside the seam? if so, release the tensions on the upper and lower loopers by a half increment only. Test again. Repeat process until tunnelling is gone and fabric is sitting flat inside the threads.

If the threads are looping off the edge of the fabric, then increase the tensions on the upper and lower loopers by a half increment only. Test again. Repeat process until the threads are sitting right up against the cut edge, and meeting right on the edge.

That is basically it - please feel free to ask me again for more help is this hasn't been clear or you still struggle with this machine. I presume that you don't have the instruction manual for it so I could scan a page or two if this will help.

This is a really good quality overlocker so don't give up on it; it sounds like you have just never been shown how to use it fully or never had the manual; consider purchasing one from Bernina or online as it is very instructive. If you find that you still struggle with getting the stitch tensions right, its a good idea to spend an hour or two with some calico and thread it up with four different coloured threads like the diagram inside the looper cover, then make stitching samples and adjust until its right. You can make a four thread, three thread wide with left needle, three thread narrow with right needle, 3 thread rolled hem and flat lock. Write down the tension numbers, stitch length and blade position onto the fabric sample and keep these in a note book for future reference. This will help you to remember what you need to change when you want to use that stitch type again.

And my last suggestion, if you can find a good sewing machine dealership or fabric store that runs classes, see if they run one for "introduction to overlockers" - I took a class from the Bernina dealer I bought my machine from back in 1992 and it was fantastic. I've used mine for bridal veils with fishing line, made table cloths, curtains, cushions, sewed dozens of knit garments for the kids and made most of my own clothes with my trusty Elna and this overlocker; its a very strong machine and better quality than many others on the market.

Most likely is the left looper thread is trapping the needle threads.

Remove the threads and start over in this sequence....

Left looper - right looper - left needle - right needle.

If you thread the needles before the lower looper, the needle thread wrapped over the looper will be under the looper thread and will never be free to form a stitch, so the threading sequence is critical.

Make sure the chain stitch thread is threaded exactly as it should be, make doubly sure the thread comes off the bobbin vertically and runs through all eyes smoothly. Any faults in the threading causes extra tension at the needle despite what the tension is set on.
If this is not the cause then the needle depth and the looper timing needs checking.
Rob