This lever has often been called an advance lever. That led to a long
discussion of what the lever is properly called. The lever is only used for
starting and is not really needed for that. Since it spends nearly all of the
time in the advanced position and when used, is retarding the timing, I call it
a "retard lever."
This photo is from an owners manual that, from the pictures of the front
fender and spokes, would be either a 56 or early 57. I think it clears up any
issue of the purpose of the ignition retard lever. Excuse my poor lighting
on the page, but using a flash reflected badly.
I should add that the R68/R69 Bosch magneto for the retard function has a
slightly different system for ignition timing. The points plate for setting the
timing is the plate that this lever operates. It may be impossible to get all of
the marks lined up correctly. Sometimes one must compromise on the timing.