Stitch issue

[Ramblinrev]

This is one of the most common conditions. You are in good company. Easy fix and something you will remember to check. Be aware that top tension needs to be checked every time you change fabrics. Different weaves, weights and fibers need different tension.

[sweetmusic]

Before actually changing tension settings, try re-threading the machine. Thread gets tension by being pulled between two metal discs in the tension assembly. When the presser foot is down, a spring presses the discs together to put tension on the thread. When the foot is raised, the spring is released and thread tension is released. You can feel the difference - sometime, try gently pulling your thread tail with the presser foot up and with it down. ALWAYS thread the machine with the presser foot UP so the thread can slip into place between the discs. If you thread the machine with the foot down, the thread may not properly settle into place between the discs. Sometimes it gets pulled into place when you start to stitch, but sometimes not - and your stitches will look as if the upper tension is too loose.

Incidentally, wee bits of fluff and gunk accumulate between the tension discs over time. Now and then floss between them with a fairly new dollar bill. The paper used in US currency has just the right texture to clean tension discs. Looks funny to have a dollar bill in the toolbox but it is one of the most useful and least expensive tools in there.

[Ramblinrev]

Before actually changing tension settings, try re-threading the machine.

While rethreading the machine is always an option and a good step to take, the pictures posted do not show what I would expect if missed threading was the issue. Generally speaking I would expect a much more pronounced imbalance if the tension had not be threaded properly. I think that's why people did not suggest that to start with. Having said that... If you had just changed the spool then the first step I would take would definitely be to rethread the machine. But according to the pictures I would say a simple adjustment to the top thread tension should resolve the issue.

Edit: The simple adjustment can be made on the fly. Rethreading the machine requires a full stop of the sewing process. It's a time management decision.