Somewhere between the knob & where it connects to the feed dog mechanism (usually closer to the knob), there is probably an eccentric that controls the stitch length. It will look like a normal screw head & you'll more than likely have to loosen a nut to turn it. Loosen the nut just enough to turn it a little, tighten & check your stitches.
I just adjusted the stitch length on a Kenmore 158 series machine & that was the set up on it. I first turned the dial to the longest stitch (6 spi on mine)...moved the eccentric a bit at a time & kept checking the length. When I was getting a perfect 6 stitches, I turned the dial to 0 to make sure that the fabric wasn't moving. Actually, I was stitching on paper (without thread)....it was easier to check the holes to count the stitches & make sure it was stitching in the same hole on 0.
If you can find a blown up picture of any White mechanism of the same era, it'll help you locate it. The eccentric was just called an adjuster on my Kenmore. It was easy to find a parts blow-up for mine though... I just checked Sears Parts Direct.
Last edited by path49; 03-03-2013 at 10:38 AM.