Question about sewing with double needle
I'm trying to help a friend who would like to sew hems on knit garments with a double needle.
Confession up front: hers is not an antique machine, but it may qualify as vintage: It's an "Elnita," and is Very Heavy -- lots of metal inside.
She had a 4.mm, size 11 needle for stretch fabric. The stitches on the top of the fabric were very good and seem secure, but they seemed to miss something occasionally on the bottom thread.
According to her manual it could be a needle size problem, and the 11 is pretty small. We also tried adjusting tension and stitch length. Since the problem was underneath, we thought the problem must be top tension, but going all the way through all choices still did not eliminate the problem (although certain settings had better results than others).
I have some photos to post, although I'm not able to indicate which sections had which adjustments.
My main question probably is: should the bobbin thread look like it is pulled completely to one side? I would expect it to have an even zig zag appearance, but don't really know, having never sewed with a double needle.
I promised her I would post photos, and that people here were very smart and could probably help!
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In the areas where we've at least managed to get a consistent stitch, even if it is not quite even as a zig zag on the back, should we call that good? Or?