Tried that and the stitching started to come undone and the thread got all tangled.
Taken from the manual...
To Regulate Length of Stitch
The machine is adjustable to make
from 6 to 30 stitches per inch, as
indicated by the numerals on the stitch
indicator plate.
The "red dot" indicator U, Fig. 24, in the
slot at the left indicates the stitch
setting. To regulate the length of stitch,
turn thumb nut V, Fig. 24, on lever
away from the stitch indicator plate as
far as necessary. Move the lever at V
until the "red dot" indicator U is at the
desired stitch setting. Then turn thumb
nut V inward until it touches indicator
plate. The machine is not set to stitch
the desired number of stitches per inch
in a forward direction.
To Reverse the Direction of Feed
For Back Tacking, raise the lever to the
upper end of the indicator plate. The
machine will then stitch in a reverse
direction, making it easy to fasten the
ends of seams.
