Peter---This subject is one that can be a matter of opinion, and
difficult to give a definitive answer. Still, we can look at what goes
on here. The viscosity of the damper oil affects how quickly the air
valve rises with throttle plate opening, and the rising is further
damped by the large, tho weak, spring. If the carbs are adjusted on the
rich side, a lighter oil might be slightly better by providing more air,
quicker. On the other hand, a "properly adjusted" carb might not like
this extra air and would respond better to the thicker oil, thereby
keeping he air/fuel mix in balance.
I base the above findings after having done several "oil" tests over
different 20 deg. to 100 deg. F climates, using an 02 sensor and
air/fuel monitor. Even then, the results never heavily favored AT
fluid, or 20W/50 oil. It seems to be a moving target. I am back where I
started, using the 20W-50 year around.
Dick Taylor
Los Angeles
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