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Re: [T3] Fw: Carbby fuel pressure


On 19 Sep 2002, at 0:13, Parker-Durost wrote:

> It calls out the pressure for both types as 4.5 psi max
> (with the outlet plugged past the gauge).  The manual says the
> pressure is directly related to the main diaphragm spring pressure.

The pressure is also a function of how far the pump pushrod rises out of the 
case. This is why you are supposed to check this measurement and adjust 
the pump position with extra gaskets. It's simply a matter of controlling 
where we are operating within the range of the spring: If the pushrod pushes 
farther into the pump the spring gets more compressed and the fuel pressure 
will be higher.

The amount of compression is also (and primarily) adjusted to center the 
excursion of the pump diaphram around the zero deflection point. This 
maximizes diaphram life.

-
Jim Adney
jadney@vwtype3.org
Madison, WI 53711-3054
USA

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