Hi, i have a Janome MC 4000. It wasn't stitching properly. I wanted to do some overlocking but it kept skipping the wider stitches. Top thread was breaking. Needles were breaking. Stitches were forming badly. I oiled it and a neat zig zag was achieved but it had skipped stitches. I unscrewed and took off the top cover and oiled there. Now the needles which fitted before no longer fit! They drag along the area where the bobbin case sits. Needles seem too long. How can this happen? The 'pole' into which the needle is clamped in seems to have lowered somehow. It needs to be raised so that the needles can fit but I don't know how. Please help.

Be sure stitch is in between the two fabrics when straight stitch. Adjust tension until stitch is between top and bottom fabric. Use different color top thread to make it easier to see. Once tension is correct sewing straight, switch to zigzag.

Remove hook race and bobbin. Clean area with vacuum.
Replace needle.
Try different thread and fabric.

Hi, I ran into this problem on a Brother Serger and if your machine is set-up for four thread overlock, this may help. Set all the tension control knobs to"3". The overlock may seem loose but see if the skipped stitches gets better or worse. Remember that the loopers are just that, they work best when the thread is not pulled tight. I found that if I took the looper tensions back up gradually, I got a pretty nice overlock at about "5" without skipped stiches.

I don't know your model in particular but generally this is how you set up a serger/overlocker to create a rolled hem. Remove the left hand needle and thread if 4 threads are threaded). Now there is usually a lever around the stitching area that you slide back towards you to remove the stitching finger back (disengaged). Then you adjust the top looper tension looser (about 2-3) and lower looper tension tighter (7 or 8). Leave needle tension at normal tension (5). You may need to move the cutting blade to the right too. The technique is to cut the fabric wider but with a narrow stitch so the cut edge rolls under within the stitching. You want the top looper thread really loose so it rolls right around underneath up against the needle thread, the lower looper thread needs to be tight and almost invisible, pulling the upper looper thread down. I usually do a few test runs and check the stitching. Once happy, I turn the stitch length right down to 1 so it is very dense. This uses a lot of thread up.

Ideally use a wooly overlock thread on the upper looper as this "fluffs" out once stitched and "fills" in covering the fabric edge completely.
some good images here
Sewing Basics Narrow Rolled Hems with Serger Sew Mama Sew Outstanding...

take it in for a service specifically the needle/ hook timing
make sure that the thread tension is correct

Normal top tension is 3-4; normal bobbin tension (iirc) is 35 grams.
I'm betting, though, that a new needle, right way around and the correct size, would solve your skipping problems.

possible problems
1) too thick for the feed dog to move the fabric forward need; lighter tension
2) are the upper and lower threads the same kind of thread?
3) is the thread feeding properly from above? sometimes the spool can snag the thread causing the tension to jump and skip stitches

MY JANOME 4400 IS SKIPPING STITCHES, ITJUST STARTED DOING THIS, HELP!!!!

To avoid skipped stitches on a coverstitch machine you need to use ELs (extra long) or SUK (stretch) needles and good quality thread. Poor quality thread is too fluffy and varies in thickness which can cause stitch problems. Try Maxilock thread from a cone or use maxilock on looper and regular sewing machine thread through needles and see if this improves the stitches. Also loosen off the lower looper tension to zero and see if this helps. If you are hemming around a garment and sewing across an overlocked seam then you need to minimise bulk too. lightly press the seams into the diretion you want them to sit when garment is finished, press the hem up, then force the seam allowance in the hem turnup area to the opposite direction. This spreads the seam bulk in both directions.
There is a knack to coverstitch machines but a good cover finish is quicker than twin needle on SM.

Rule of thumb: Fast needle, slow hands. This should help. GiGi

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