Every machine quilter deals with puckers eventually, including the ones who've been at it for years. A pucker is a small fold of excess fabric that gets caught and stitched down where it shouldn't be, usually on the backing, and a tuck is the same thing at a smaller scale — a tiny pleat that sneaks into a seam or a curve. Neither means you've ruined anything. Both are fixable, and once you know the handful of causes behind most of them, they get a lot less frequent.
Tight top tension
If your top thread tension is set too tight, it pulls the top layer of fabric slightly toward the stitching line with every stitch, and over a long seam that small pull adds up to visible puckering along the line, even on a well-basted sandwich. This is worth ruling out first because it's an easy fix: stitch a short test line on a scrap sandwich made from the same fabrics, batting, and thread you're using on the actual project, and check both the front and the back. If the stitch line looks tight or the fabric is cupping slightly around it, back your top tension off slightly and test again before continuing on the real quilt.
Basting that let the layers shift
This is the single biggest cause of puckers, more than any other factor. If the top, batting, and backing aren't held firmly together, they can shift relative to each other as you feed the quilt through the machine — the backing especially, since you usually can't see it while you're stitching. A basting job that's too sparse, whether that's pins spaced too far apart or a thin, uneven layer of spray baste, leaves room for exactly that kind of shift, and shift is what turns into a pucker on the back of the quilt that you don't notice until you flip it over.
Quilting too fast for the feed rate
Both straight-line and free-motion quilting have a feed rate the layers can comfortably move at without bunching. Pushing the machine faster than that — whether that's flooring the pedal on a walking-foot line or trying to move your hands faster than they can steer cleanly in free-motion work — outruns the fabric's ability to move smoothly through the machine, and the excess gets pushed into small folds instead of feeding through flat. Slowing down is rarely the answer people want to hear, but it's consistently the answer that works.
Not smoothing the sandwich outward first
Before the first stitch goes in, the quilt sandwich needs to be smoothed from the center outward in every direction, working out any slack or looseness in the batting and backing before you pin or spray-baste it down. Basting a sandwich that already has loose, unsmoothed slack in it locks that slack into the quilt permanently, and it tends to surface as a pucker exactly where the looseness was worst. This step takes real floor or table space — you can't smooth a sandwich properly bunched up on a small table — and it's tempting to rush past it, but it's doing real structural work.
Fixing a small tuck
For a small tuck — a pleat an inch or two long — use a seam ripper to carefully remove just the stitches over that section, working from the back where you can usually see the fold more clearly. Smooth the layers flat again by hand, working the fabric from a few inches on either side of the tuck toward the gap, then re-pin or add a small dab of spray baste right at that spot before re-stitching over the same section. Small tucks caught early are genuinely quick fixes, usually a few minutes of work.
When to start a section over
A bigger pucker — one that runs several inches, involves a real fold rather than a small pleat, or that you only discover after quilting a large area around it — usually isn't worth unpicking stitch by stitch. At that point it's faster and it produces a better result to unpick the entire section of quilting back to a clean starting point (a seam line or the edge of the design), re-smooth and re-baste that whole area properly, and re-quilt it from scratch. Trying to patch a large pucker in place, rather than redoing the section, tends to leave visible unevenness even after the fix.
The line between "pick out this one tuck" and "redo this whole section" is roughly the size of the problem: small and isolated, fix it directly; large or the sandwich clearly shifted underneath, start that section over. Either way, basting more generously before your next project is the actual prevention — not a faster hand with the seam ripper. It's tempting to treat basting as the boring part standing between you and the quilting you actually want to do, and to rush it accordingly. In practice it's the cheapest insurance in the entire process — pins spaced every four to six inches, or an even, well-covered layer of spray baste, cost a little extra time up front and save far more time later in unpicking and re-quilting. Quilters who baste thoroughly report puckers far less often, not because they've developed better machine skills, but because the layers simply have nowhere to shift once the needle gets there.