Why does my decorative stitch look wrong?

Most decorative stitch problems are support problems rather than tension problems. Dense stitching pulls fabric in, and fabric that is not held cannot resist it.

Stabiliser first. Put a tear away stabiliser under wovens and a cut away under knits. Without one the fabric tunnels into a ridge beneath the stitching, and once it has tunnelled there is no fixing it.

Then the foot. Use a satin stitch or open toe foot, which has a channel underneath so the raised band of stitching passes freely. A standard flat soled foot rides on top of the stitching and drags it, producing an uneven result that looks exactly like a tension fault.

Then tension. Decorative stitching normally wants slightly looser top tension than construction sewing, so the lock is drawn to the underside and the bobbin thread does not appear along the edges. Half a number is usually enough.

Then thread. Rayon and cotton embroidery threads give a better sheen than general purpose polyester, and a finer bobbin thread reduces bulk on the back.

Speed. Slow down. Many decorative stitches involve reverse motion and sideways feed, and they need time to form correctly.

And test the full pattern on a scrap with the same stabiliser. A pattern that repeats every 3 cm cannot be judged from 1 cm of stitching.

One more. Check the machine can complete a pattern repeat before the seam ends, or the line finishes halfway through a motif.