On Wed, 16 Aug 1995, JAMES wrote:
> Graham wrote,
>
> >What is the theory of operation on an SU Carb??
>
SU's are _so_ _cool_! The vacuum that raises the piston is piped from
the side of the throttle plate away from the manifold. So when you open
the throttle, you get vacuum which raises the piston, which raises the
tapered needle in the jet, letting more fuel into the incoming air
stream. Oil in the damper prevents the piston from rising too quickly,
so you get a brief period of rich mixture because the fuel is pulled from
the jet by the vacuum and the piston being down prevents as much air from
getting through. Voila! Accellerator pump action without the pesky
accellerator pump! The jet/needle combo is designed to let enough fuel
come through for idling and the float keeps the fuel level in the jet
relatively constant.
Kevin Sullivan -- 1960 MGA
Nichols Research Corp.
Shalimar FL USA
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