What a List!!
Thanks - to all contributors!
Dave (long retired ME, with a vague recall of venturis, Bernoulli, etc.)
'68 1600
Kailua-Kona
Brian Hollands wrote:
> >The thinner the oil the quicker the piston moves up which takes the
> needle
> >with it, thus moving the lower thinner part of the needle to the fuel
> >dispersal area of the jet providing a larger orifice area
>
> Half correct -
> The oil weight has (essentially) no effect on how high a given amount of
> vacuum will lift the suction piston, only how fast it will lift it.
> Remember the way an SU or Stromberg (CD, Constant Depression - in
> American English "constant vacuum") carb works is by varying the venturi
> size so as to keep the velocity of air moving through it constant. Thus
> the vacuum seen at the fuel nozzle is also constant. The exception to
> this is when the engine needs to accelerate. In order to accelerate an
> engine, the mixture needs to be richened (that's why other carbs have
> accelerator pumps). In the SU type carb what happens is the damper
> oil's resistance causes the suction piston to rise more slowly than it
> otherwise would which (bertouli's principle) causes the speed of the air...
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