janeite,
I doubt the cam stack is out of time. It would take major damage or a 3 year old grand son to mess it up that bad.
Here is a pic of the cam stack:
Notice the slots in the vertical shaft the arrow is pointing to. Each of these slots correspond to a cam. There are two of these shafts, one front and one rear. Each has a sliding part that is raised and lowered by the round nobs. At each position a lock tab snaps into a slot. If the locking tab does not snap into the slot the cam follower is not on the cam right.
These two areas must be free to move as the nobs are turned. Concentrate there.
Here is what my 401A did just yesterday:
The far left is 7 rows of straight stitches reducing the stitch length one number at a time.
From there each pattern corresponds to the basic chart under the trap door. The zig-zag is BL with the red lever at 5 and the stitch length at about 15. As I moved through each pattern as indicated on the chart I gradually tightened up the stitch length to about 25 or so. That is in the "fine" area. But for that you need a satin or special presser foot.
From the straight stitch three patterns to the right of the bold one the patterns are the cams. For those the red lever was set at 3 and the stitch length was still at 25.
You'll notice if the pics are clear enough on your monitor that it skipped a few stitches at first. Also I can't sew a straight line very well.
I'd clean that cam stack and all the moving parts that work with it and make sure they all work properly and smoothly before you mess with the stack timing.
Just for my info, where did you find the manual for timing the stack?
Joe