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On 6 Jan 2003 at 20:49, Carver wrote: > Bear with me if any of the following is gibberish. > > The mechanical fuel pump is actuated by a cam. > The action of the cam going up would provide the > pressure to force the fuel to flow. The spring > is there simply to push the diaphragm back down > for the next up/pump cycle to follow the cam. > The spring is responsible for drawing fuel into the > pump, not providing the pressure out to the carbs. I realize that this is the most obvious solution, but it's not the way it works. The pump's upstroke, driven by the cam, is the intake, which means that the pump always gets driven to the top of its travel. The downstroke, driven by the spring, forces gas to the carbs at a pressure determined by the spring. Under most conditions, the diaphram returns only a small fraction of its total possible stroke before the cam pushes it back to the top again. Thus the pressure is determined by the pump (spring.) Otherwise there would be 2 problems: 1) The pump would try to force gas to the carbs even when the float valves were closed. 2) The pressure would vary from zero (when the cam was on the downstroke) to infinity (when the pump was on the upstroke and the float valves were closed.) -- Jim Adney jadney@vwtype3.org Madison, WI 53711-3054 USA ------------------------------------------------ To unsubscribe, E-mail to: <type3-off@vwtype3.org> For more help, see http://vwtype3.org/list/