Congratulations and welcome to Quilting Board. From what I could see in the videos, the scarf was in the right position for the hook to catch.
Yes, the knobs are to limit the width of the zigzag.
Have you oiled top and bottom and the needle bar area? Sometimes the needle bar needs to slide to allow for zigzag stitches.
There is a manual for a White 1268 which is very similar to the Universal on the singer.com support site. It is not great, but may help. The manual shows a low shank foot, but I think the Universal is a high shank foot. The direct link is
https://res.cloudinary.com/singer-se...ite-1268-x.pdf
Janey - Neat people never make the exciting discoveries I do.
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