Running rich!

[bobcowan]

The fuel pump does not control the pressure. It just pumps fuel. Pressure is created by restrictions after the pump. Just like putting your thumb on the end of the garden hose.

If you're measuring >10psi at the carb, then there's enough restriction at idle to create that pressure. Make me wonder what the pressure is at WOT under a load?

A failing pump will move less and less fuel, and the pressure will drop. Doesn't sound like that's happening here.

I would add a return style pressure regulator as close as possible to the carb inlet. Maintaining a steady pressure with the proper volume is pretty important.

[Tommy]

Originally Posted by bobcowan

The fuel pump does not control the pressure. It just pumps fuel. Pressure is created by restrictions after the pump.

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.

[Gaz64]

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.

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.

[TKlauber]

Well both fuel pumps arrived today. Same pump, one from Jeggs and the other from Summit. They are handsome Carter M6905 units and made in USA!
The weather has turned cold here as anticipated. I will try and get one on this week and report back. I will have to put the car up on jack stands and will also change the oil and filter in case there is too much gas in the oil. I may spray paint the black side pipes while it is up in the air if the temperature is high enough to paint.