Last updated: August 21, 2026
The serger was fine last week. Today the stitch has a gap in it every inch or so, or one thread is lying on the surface in loose loops instead of wrapping the edge, and the seam pulls apart when you tug it. Nothing has changed except the fabric, or the color of the thread, or the fact that a week has gone by.
That is almost always good news. Skipped stitches and loose loops on a serger come from a short list of causes, and the first four cost nothing to fix. Work through them in the order below rather than starting with the tension dials, because tension is the thing people reach for first and the thing that is least often actually wrong.
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Quick Answer
Why is my serger skipping stitches and leaving loops?
- Rethread the whole machine in the order the manual gives, with the presser foot up so the tension discs are open.
- Fit fresh needles of the system your manual specifies, pushed all the way up, flat side to the back.
- Use a ball point needle on knits. A sharp point in jersey is the single most common cause of skipping.
- Only then look at tension, and clean the lint out from under the plate while you are in there.
Bottom line: threading and needles fix the large majority of these faults, and both are free. Turn the dials last.
Start by Reading the Stitch
Before you touch anything, sew a sample on scrap of the same fabric and look at which thread is misbehaving. A gap in the seam line points at a needle thread. Loose loops hanging off the edge point at a looper thread. Loops on the top surface and loops underneath mean different things, and telling them apart saves you an hour.
Trim the sample so you can see the wrap. If the whole wrap is loose but even, that is tension. If the wrap is fine and a stitch is simply missing at intervals, that is a needle or a threading fault, and no dial will cure it.
Step One: Rethread the Whole Machine
Rethread completely, in the order the manual gives, which on most machines is upper looper, lower looper, right needle, left needle. Do it with the presser foot raised, because the tension discs only open when the foot is up and a thread laid in with the foot down sits beside the disc instead of between the two halves.
Take the threads out rather than pulling new ones through, and check each guide as you go. The guide people miss most often is the last small hook just above the needle, and the one on the underside of the take up area. Our threading walkthrough goes through the order step by step.
The Detail That Catches Everyone
If the loopers were unthreaded, the needles have to be threaded last. Thread a needle before the loopers and the needle thread ends up trapped under the looper thread, which produces a stitch that looks nearly right and falls apart the moment you pull it. When in doubt, cut all four and start again from the top.
Step Two: New Needles, Correct System
Fit new needles even if the current ones look fine, because a bent needle is often invisible to the eye and a blunt tip does not show at all. Use the system your manual specifies, push each needle up until it stops, and tighten the setscrew properly with the machine switched off.
A needle that is a millimeter short of the top of the needle bar puts the eye out of position for the looper, and that is a skipped stitch every time. Which system your machine takes is covered in our serger needle guide, and the general rules on points and sizes are in the needle guide.
Ball Point for Anything Stretchy
If the machine only skips on jersey, interlock, rib or French terry, the point shape is the cause. A sharp point severs a knit loop instead of sliding between them, and the resulting hole is not a clean channel for the looper thread. Fit a ball point in your machine’s needle system and sew the same sample again.
Step Three: Suspect the Thread
Cheap cone thread is the cause people resist the longest. Weak or fuzzy thread stretches under looper tension, snaps back, and drops the loop before the needle arrives. It also sheds lint into the tension discs, which then gives you a second fault on top of the first.
The test is quick. Snap a length between your hands. Good serger thread resists and breaks cleanly, poor thread stretches and fluffs. Old thread from a drawer that has spent summers in a hot room fails the same way even if it is a good brand. There is more on what to buy in our serger thread guide.
Step Four: Then Look at Tension
Only now do the dials come into it. Reset every dial to the number in the manual for the stitch you are sewing, then change one dial at a time by a small amount and sew a sample after each change. Changing two at once means you no longer know what did what.
Read the stitch to know which dial to turn. Thread lying flat on the top surface means the upper looper is too loose or the lower looper is too tight, and the reverse if the loops are underneath. The needle threads only affect the seam line itself, not the wrap.
Matching the Symptom to the Cause
Use the table as a shortcut once you have read the stitch. It follows the same order as the steps above, so the first check in each row is the free one.
| What you see | First check | Second check | Usually turns out to be |
|---|---|---|---|
| Stitch missing every inch or so | Needle new, fully seated | Needle point suits the fabric | A blunt or wrong point needle |
| Skips only on knit fabric | Ball point needle fitted | Differential feed set above one | Sharp point cutting the knit loops |
| Loose loops off the edge | Looper threads seated in the discs | Looper tension dials | A thread that missed a tension disc |
| Seam pulls apart when stretched | Threading order, loopers before needles | Needle thread tension | Needle threaded before the loopers |
Lint, Feed and the Things Under the Plate
A serger makes more lint than a sewing machine because it is cutting fabric while it sews. Switch the machine off, open the looper cover, and brush the lint out of the tension discs, the feed dogs and the knife area. Compressed air blows debris deeper into the machine, so a stiff brush is the better tool.
While the cover is open, look at the knife edge. A dull or chipped knife leaves a ragged edge that the loopers cannot wrap cleanly, which reads as messy stitching rather than skipping. Knives are a wear part on a serger and your manual will say how to change or adjust yours.
What Not to Do
Do not open the electrical side of the machine, and do not go near the motor, the wiring or the foot pedal internals. Timing adjustments between needle and looper are also a workshop job, not a kitchen table job, because they need a gauge and they are easy to make worse. If threading, needles, thread and cleaning have all failed, that is the point to read when to take it to a repair shop.
Frequently Asked Questions
Why does my serger skip stitches only on knits? Because the needle point is wrong for the fabric. A universal or sharp point cuts knit loops instead of parting them, and the hole it leaves does not present a clean loop for the looper. A ball point in your machine’s needle system fixes it in most cases.
Can bad tension cause skipped stitches? Rarely on its own. Tension changes how tight the wrap is, not whether the looper catches the thread. A stitch that is genuinely missing is a threading, needle or timing issue, so work through those before you turn a dial.
Do I have to rethread from scratch every time? If the fault is a mystery, yes. Rethreading in the correct order with the presser foot up takes a few minutes and eliminates the most common cause. Once the machine is running, you can change colors by tying new thread to the old tails instead.
Could the needle be in backwards? On most home sergers the needle has a flat back and only goes in one way, but on machines where the shank is round it can be rotated slightly, and a few degrees is enough to cause skipping. Check the manual for the orientation your model wants.
When is it a repair shop problem? When fresh needles of the right system, a full rethread, decent thread and a clean under the plate all fail. Timing between the needle and the loopers can drift after a hard jam, and that is a service adjustment.
The Bottom Line
Work in order and you will usually be sewing again inside twenty minutes. Rethread with the foot up, loopers before needles. Fit fresh needles of the right system, all the way up, ball point if the fabric stretches. Test the thread by snapping it. Clean the lint out. Change one tension dial at a time, last of all. Read next: our serger needle guide for the system your machine takes, and the needle guide for point shapes and sizes.