Hi Blue and Gadge,

I was just passing through.
The link to the Historical Record for the Model 320
does show the recommended mix as being 1/2 pint to 1 Gal.

Blue asks an interesting question, and Gadge's reply is probably correct -
ask an engineer of the time. But ...

There may have been inconsistent quality control in earlier times,
with fuel in particular. I have seen records expressing concern about
some consumers not understanding more complex ratios, and also the difference
in the 4-cycle engines folks had become accustomed to, and the two strokes.

A second reason may be about quality control within the engine itself.
So, I speculate that the ratio was a fall-back simple ratio to be safe, rather than sorry,
and probably grounded in the history of quality control for oil, fuel and engine production.

In reference to the Midgets, this was the ratio for early two-strokes, but I note that in my
Villiers Midget book they recommend 20:1 once the engine was run in:-
[Note the concerns about oil brands and adequate mixing]

[Linked Image]

Cheers
---------------------------
JACK.