Machine straight stitch with regular zigzag stitches.

[MorriganManor]

I have just started to use an old Janome machine I inherited. It’s about 40 years old, but hardly used, kept in pristine condition, all parts oiled and working smoothly etc.
It’s making a stitch pattern in the shape in the attached diagram. Using ordinary cotton, Guterman thread. Tension set as required for straight stitch and I have also tried altering the tension slightly.
Bobbin wound correctly. Machine threaded up properly. Needle changed for a new one (again, pristine condition, kept in case, never used).
I’m not dragging the material through, or going too fast.
What could be going wrong?

No, I haven’t had it serviced. I was going to have it looked at if it seemed ‘sticky’ etc when sewing but it it’s honestly so smooth when running. Does look like the dials being stuck could be the thing, so I’ll find somewhere to have it serviced.

Have you done a row of stitching on each setting?

Button hole through A to F?

I have a very similar Janome. Are you sure the second dial isn't accidentally pointing at the stretch stitch? I would do a test on all the stitches too.

Setting the first dial to B gives a perfect straight stitch! It obviously needs a service as suggested. Silly of me to assume that because the rest of the mechanisms were running smooth as butter, rust free etc that the dials would be fine too. 🤦‍♀️
I will run through all the stitch settings this week and make notes of what works as it should and what doesn’t.
Good old MN, I knew I’d get some excellent advice

at least you can sew a straight stitch now!

Glad to hear you figured it out! One last tip: if you store your machine in an unheated space you should set it up in a warm room for a few hours before sewing. The machine oils can get thick with cool temperatures and non-use . This will help it function better.

Do have it serviced if it has been a very long time since it was used.

Happy sewing. ;)

It’s a very neat little straight stitch too!

Update: a cushion cover! Not perfect by any means, but I’m pleased with my first machine sewing attempt in 35 years! Matching stripes for a first project maybe not ideal but it’s got me in the swing of things again.
Looking for someone to service machine now, so I’m not compensating for the shift to the left of the needle.

That's great! You ought to be very pleased with yourself - especially the stripe matching!