2 1/2 psi fuel pressure

[drolston]

Originally Posted by Tinker

Charlie, what are your thoughts on putting an extra gasket under the pump to lower pressure?

Raising the pump would lower the stroke and therefore the volume capacity of the pump, but the effect on pressure at the no/low flow condition is complicated. No-flow pressure is not really determined by the strength of the valve springs, but by the flexibility of the pump diaphragm versus the volume of the pump stroke. If fuel outflow is blocked by the carb float valve, the only place for the fuel in the pump chamber to go when the center of the diaphragm is pushed up by the pump rod is for the outer part of the diaphragm to "balloon" down a little. Because the pump volume for each stroke is pretty low (maybe a tablespoon?), it is not much of a stretch for the diaphragm.

Because the pump diaphragm up stroke (pressurizing) is on the down stroke of the push rod, the strength of down spring of the pump lever would theoretically limit pump pressure. That spring also keeps the pump push rod from floating off of the cam at high rpm. I am guessing that the Ford engineers have that spring just high enough to avoid that problem. Interesting physics problem for this winter. I will report back.

I recommend keeping the pump at full stroke and using a pressure regulator. Grosse type float valves have worked well for me to over 4 psi.