Well...
I think there's a reason for those different
recommended needles for the stock engine in the factory manuals or they
wouldn't bother listing them?
(Then again, they're British so maybe they would!. :).
The SU is a "constant VELOCITY" carb.
"Volume" increases as air valve rises
but "density" of air depends upon "density" altitude (pressure altitude
corrected for temperature....they haven't found a way to correct for relative
humidity far as I know).
So a cubic foot of air at 5.000 feet contains
less "air molecules" than a cubic foot of air
at sea level.
Layman's terms..."what it all means".......
Here's what Burlen told me: "Weak" needle
is basically for motors run at/over density altitudes of 3.000'.
"Rich" needle for "drive it like you stole it"
WOT/redline types, or if you're running lower than recommended octane
(combustion cooling) or maybe you're running slightly higher than stock
compression ratio or added a header and maybe free-flow air filters, etc.
Anyhow, that's what they told me. Do I
"know". No. My area of expertise is safe civilian airplane driving within a
controlled civilian environment.
Always willing to learn though and welcome
knowledge, remarks from others 'cause maybe I heard wrong or misunderstood.
Cap'n. Bob '60 :{)
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