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PostPosted: Tue Dec 12, 2017 5:43 pm 
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The diaphragm wore out in my stock '63 fuel pump (Carter). Everything with the carburetor (stock) had been working OK up until the pump failed. I rebuilt it with a kit from Then & Now Automotive and reinstalled it. The engine ran at choke, then idled normally for about 15 minutes. Then the RPMs dropped and the engine stuttered. Goosed the accelerator and it smoothed out and ran normally. Then it happened again. Happened twice more, then the carburetor literally overflowed with fuel.

I thought there might be grit or sediment that had been pulled into the carb by the newly-rebuilt pump, possibly clogging it, so I pulled it and rebuilt it (feeling like it was overdue anyway) with a kit from Daytona. Reinstalled the carb and the same thing happened: overflow.

Pulled the carb and inspected the floats: they aren't taking on fuel and the newly-designed Daytona float valve (their replacement for the stock needle & seat design) seems to be seating correctly. Made sure the floats were adjusted to provide correct fuel level in the bowl.

I've never had this problem before. My next step is going to be to check fuel pump pressure. Don't know how it could be that, but I didn't have any problem with the carburetor until I reinstalled the rebuilt fuel pump.

What's the best way to check fuel pump pressure when the car isn't running? Is there a way to check tension on the main spring to gauge the kind of PSI it will output?


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PostPosted: Tue Dec 12, 2017 6:38 pm 
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Disable the ignition by removing the + primary wire from its threaded post on the ignition coil and taping off the end of the wire. Put your pressure gauge securely on the top end of the fuel line (where it normally attaches to the carburetor). Crank the engine and see what the gauge reading builds to; you're looking for 3 to 5 psi.

I think the problem's probably with the inlet needle/seat, but make sure the float hinge pin retainer is in place.

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PostPosted: Thu Dec 14, 2017 2:45 pm 
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Thanks for the tip Dan. Going to have to get a fuel pressure gauge to test.

I'm wondering if the new Daytona float valve needs additional compensating on the float tang to keep the correct fuel level in the bowl. A small leaflet accompanying the carb kit goes into much detail about how their new float valve is far superior to the stock design, yet they say nothing about needing to deviate from spec stock float crown-to-fuel-bowl-surface level because their valve runs fuel in the bowl leaner with a much shorter open.


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PostPosted: Thu Dec 14, 2017 5:37 pm 
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You shouldn't need to change the float adjustment from spec, but you do need to check it at every rebuild, even with an ordinary-type inlet needle/seat. That raises an important question: how did you check and adjust the float level? Carb kits, no matter where you get them, don't come with usable float gauges any more. Now you just get a completely useless strip-of-paper ruler. See here.

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PostPosted: Sat Jan 06, 2018 4:28 pm 
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SlantSixDan wrote:
...That raises an important question: how did you check and adjust the float level? Carb kits, no matter where you get them, don't come with usable float gauges any more. Now you just get a completely useless strip-of-paper ruler. See here.


Yes, checked at every rebuild. And yes, no useable float gauge which has always confounded me. While in the past I have trailer-trash eyeballed it (and probably paid for my lack of preciseness in fuel economy and performance), this time I drew a gauge on paper, measured precisely for 7/32" and glued to a gasket backing cut to size. Still a mickey-mouse job, but better than what I was doing.

I should have gone with my gut and the most obvious problem from the get. Upon testing, the newly-rebuilt fuel pump is reading 10-12 PSI when cranking and while running badly with a dripping carburetor, about the same.

The new pump diaphragm spring is too strong and it's pushing past the new fuel inlet valve, flooding everything. :evil:


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PostPosted: Sat Jan 06, 2018 5:30 pm 
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Gross! They sent you a diaphragm assembly with the wrong spring. I'll be surprised if they don't step up and make it right.

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PostPosted: Sun Jan 28, 2018 2:17 pm 
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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! :evil:

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!


Attachments:
Then & Now Auto Fuel Pump Rebuilding Guide-Too Much Pressure.jpg
Then & Now Auto Fuel Pump Rebuilding Guide-Too Much Pressure.jpg [ 97.15 KiB | Viewed 619 times ]
Carter Carburetor 1955 Bulletin.jpg
Carter Carburetor 1955 Bulletin.jpg [ 119.74 KiB | Viewed 619 times ]
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PostPosted: Sun Jan 28, 2018 3:19 pm 
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The pressure is determined by the diaphragm spring, not the valve springs. Assuming your pump is an original, it's a Carter M-2996s and that's what you need the kit for. Call 'im back, tell 'im you've still got 15 pounds, and ask him to please actually check the spring pressure on the next one he sends you.

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PostPosted: Sun Feb 18, 2018 11:45 pm 
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"All's well that ends well.." and "3rd time's the charm" as they say.

Had to go back and forth with Then & Now Automotive, and on the third try and after at least two conversations with their engineer, they sent a diaphragm with a different spring that had the correct pressure, which worked as soon as I installed it.

Hallelujah. Only took four months of on-again-off-again working on it to get it right. :roll:


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PostPosted: Mon Feb 19, 2018 9:13 am 
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Hoorah for persistence. Glad they finally owned it and fixed it.

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