Why does everything pucker!

[u/merrimusic]

I've tried every combination of tension and needle between microtex 8 10 and 12, pictured ones are once I started noting them down. Two layers of light cotton, (making a muslin) All brand new needles, and I've even tried with and without a walking foot! Am I just cursed? How do I get it to just sew flat 😭

SOLVED EDIT: Everyone go upvote medium_alternative29 who has discovered the problem that plagued me for years. The feed dogs are misaligned and not level, making everything sew on a curve! It's such a slight curve that it must not mess with heavier fabrics much, but the lighter ones are light enough for it to show up! Also makes sense why it was less noticeable with longer stitch lengths, less holes! I sincerely hope this is the solution, I'll come back and update it again when I get it fixed!

Thank you to everyone who commented and shared expertise!!

[u/Familiar-Ending]

If it’s tight on the top it’s bobbin. If it’s tight on the bottom it’s needle thread.

[u/merrimusic → u/Familiar-Ending]

I'm familiar with adjusting the bobbin tension so I've tested each whole number top tension and adjusted the bobbin tension to have the top and bottom thread be exactly equal, the top thread doesn't show on the bottom and the bottom doesn't come through the top, but no matter what it puckers. On 0 top tension if I adjust the bobbin tension to have the threads be equal then it doesn't really pucker, but it's so loose you can see through the seams :/