Update: I’ve isolated the problem to the fuel pump and an over-abundance of pressure, as per my last post, it’s over double the recommended amount. Through a small battery of tests, I have made very sure it is NOT the carburetor that is the issue.
The first time I rebuilt the pump, Then And Now sent me a diaphragm with spring assembly, a new pulsator gasket, and a new pump-to-engine gasket. Installed all, and the high-pressure was still there. So I called them back and spoke with the owner. We double-checked the pump casting numbers and he sent me an entire kit. Here’s where it gets confusing.
Pulled the spring and seal off the first new diaphragm assembly, and replaced it with the spring from the second kit, per his recommendation. Looked at the check valves and springs but they seemed fine so I left them alone. Re-installed the pump and the pressure is still high. Yanked it off again, and re-read his instructions, and the recommendation for pressure that’s too high (see the attached picture), is likely the check valves. So I pulled the check valves, installed new springs and new Viton seals. Upon installation of the new springs and seals, I felt sure I had finally discovered the issue, because the new seals moved up and down on the umbrella stems so much easier than the old ones, which seemed to have swelled on the stems and were binding, something I hadn't noticed before.
Put everything back together, and lo and behold, the cranking and operating pressure is still nearly 15 psi and the carb is still overflowing! 
The only thing I can think to do now is to yank out the first replacement diaphragm they sent, remove the spring and re-install it on the second diaphragm that came with the spring. The edges of the newest diaphragm are key-notched, unlike the old one and the first replacement. Aside from this visual difference, the material thickness between the two new diaphragms looks the same.
I have a note from the owner of Then And Now that stemmed from our discussion about how to measure fuel pressure. He cites a Carter Carburetor Corp bulletin from 1955 (attached). In this article, they state to be sure that the hose between your T-valve and the meter is NOT longer than 6” or it will give you an abnormally high reading. Then And Now states you cannot measure pressure any other way or you won’t be getting accurate results the way Carter intended.
Well….OK. My response is, but this bulletin was printed in 1955 and diagnostic equipment has evolved. The diagram in their bulletin shows a simple T-valve, hose and meter. At that time, there was likely no special pressure regulating valves within the less-than-6”-hose, it was probably all at the meter end and the short hose was to minimize fuel pulses affecting meter read.
I’m measuring my pressure with a T-valve, and a modern Actron fuel pressure meter. Which has a very long (much longer than 6”) hose from the T-valve to the meter head. The hose has pressure regulating fittings where it screws to the T-valve. My understanding of Actron’s gauge is these fittings help smooth out the fuel pulses to the liquid-filled meter. But the issue, according to the owner, could possibly be that I’m not following Carter’s pressure-measuring procedure, so I'm comparing apples-to-oranges.
Again…well, OK, but the fact is, my carburetor is still overflowing, so I still have too much pressure.
Sorry for the book. Does anyone have any other ideas? Something I’ve missed? I'm at my wits end!
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Then & Now Auto Fuel Pump Rebuilding Guide-Too Much Pressure.jpg [ 97.15 KiB | Viewed 4731 times ]
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Carter Carburetor 1955 Bulletin.jpg [ 119.74 KiB | Viewed 4731 times ]
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