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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. If this is an accurate summary of the action, then the pressure is a result of the throw of the cam, not of the strength of the spring. The lengthening of the spring would be to compensate for the longer throw of the cam on a T3 versus a T1, not to provide extra pressure. The lack of an adequate spring might manifest itself with a slower intake of fuel into the pump though. If this is the case, it's not the fuel pump that is unique, it's the cam driving it. Perhaps a different diameter diaphragm is the cause of the different pressure. I could easily be way off, or just plain ignorant. Jeff '67 Sqbk -----Original Message----- Once the pump fills the carbs, the pressure should not vary with RPM. ------------------------------------------------ To unsubscribe, E-mail to: <type3-off@vwtype3.org> For more help, see http://vwtype3.org/list/