washing does wonders, but "viscose" scares me. doesn't sound like a stable quilting thread. sounds like it will melt away. Just an odd thought ;-)

Rayon thread isn't as strong as cotton or poly, but I have used on my DSM when the color was right. I know nothing about quilting machines, but my first thoughts when I read your post were that the needle is too large for the fabric or it has a tiny burr on it. I'd try a new smaller needle or at least a new needle in the size your machine likes. I use a new 12 for each quilt.

Thank you. The holes have disappeared on the tiny bit I've unpicked so far and I'm sure they will disappear on the bits I'm leaving. Unpicking is proving very time consuming as the design is double stitched so each stitch needs snipping

Interesting info. Thanks. By the way, does anyone know the quilting stitch and settings to use on a Janome 6600? I'd appreciate the help.

I have a Topaz 20 and am using embroidery patterns to quilt inside Rings that Bind quilt blocks. I am using 40wt embroidery thread with a quilting needle. I tried the embroidery needle and it didn't look good on the back. When I used the quilting needle the back looked as good as the front. I don't know why the difference but it works. I can see light thru some of the holes but when I wash it and it puffs up and crinkles I am sure the holes will close up.

even when you sew on your dsm you can see needle holes after washing they usually close up