I tried to stop myself and Failed!! Here goes...
Higher Altitude = Less Pressure + Less Air
SU's are a constant depression type device. The piston is basically a loaded
aerofoil, lifted by the air density flowing through the throat and loaded down
by the spring. x cc's of air per sec gives y mm lift of piston.
Less Air = less lift = lower needle position = leaner mixture than at lower
altitude = self compensating (to a degree!!)
The function of the oil in the damper section of the is the stop the piston
from
flying up on sudden throttle openings, and from fluttering at low idle.
On the other hand, I could be completely wrong!!!
Dave Gropper, '73 MGB (no oil to rockers, working on it..again!)
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