Quote:
Originally Posted by Tommy
Bob,
I admit I don't know much about the design of mechanical fuel pumps, but it seems to me that the restriction you allude to is the float valve in the carb. The problem is that when the valve is closed the pump is powerful enough to raise the pressure above the target 5-7 PSI. My guess is that there is a spring controlled bypass valve at the pump that is supposed to open and release excess fuel back to the intake side of the pump. I consider that to be part of the pump, so by my definition the pump does control the pressure and the OP's pump is bad. .. True, a pressure regulator and return line can solve the problem, but so can a properly functioning fuel pump.
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Yes, that is near correct. In a mechanical fuel pump, the diaphragm spring determines the maximum fuel pressure. When volume requirements are low, the fuel diaphragm travel oscillates slowly, and the rocker arm linkage has a spring to allow the cam actuator linkage to follow the cam without moving the diaphragm. As the engine demands more fuel, the diaphragm oscillates more.
If you have high fuel pressure, the pump is the cause. Yes, you can limit the pressure at the carb with a deadhead or bypass regulator, the later needs a return line to the tank.