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> Mike, I have the manual. So far it reads like greek to me. As for the
> really strange gasket with the button thingy. The button almost seams like
> some sort of a valve or pressure release or something. it would seam that
> just replacing it with a gasket would defeat whatever its purpose is. Is
> this a necessary item? Next question, could someone explain to me what the
I would hazard a guess that it is necessary, at least as a gasket-type
thingy. I have no experience with the ZS carbs, but those
appurtenances weren't put there to reduce cost!
> differnence is between a normal carb and a constant depression carb. And
> why do we put oil into it? Thanks,
The constant depression refers to the fact that these carburettors
operate with a constant reduction in pressure applied to the
fuel-metering jets.
In contrast, variable depression carbs, such as you might find in
US-built vehicles (Holly, Carter, et.al.,) the depression (the
pressure difference developed across the venturis) varies with the
amount of air that flows through those venturis.
In the SU (and presumable the ZS, since you are asking about them),
there is a spring-loaded piston and a jet "bridge", the gap between
which a vacuum (depression) is developed by the flowing air. This
depression is held constant by a spring-loaded piston, which balances
the difference in pressure between atmospheric pressure (acting on the
small area of the piston) and the air pressure downstream of the jet
body (which is applied to the large area of the piston via a passage
into the bulbous chamber above the venturi area.)
The oil just provides control of the damping so the piston doesn't
oscillate up and down. If it did, the average depression might be
constant, but the mixture and the depression would vary all over the
place as the area that the air flows through varied with the motion of
the piston. You can try leaving the oil out; I suspect the behaviour
of the carb would be instructive (if the engine runs enough that you
get to watch the behaviour.)
(Try holding a weight on the end of a "Slinky", and you'll see how the
piston would oscillate. Now imagine that that piston is moving your
mixture control needle from rich to lean and back again, and you'll
begin to see what the engine might have to deal with.)
Donald.
> Patrick
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