Seal Tested WO-A8323 Fuel Pump

1941 - 1945, MB, GPW Technical questions and discussions, regarding anything related to the WWII jeep.
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tsmgguy
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Seal Tested WO-A8323 Fuel Pump

Post by tsmgguy » Tue Feb 07, 2023 8:04 am

Pandemic disuse and bad fuel left my '43 MB with a stuck valve that could not be freed up with the penetrating oil trick. Off came the head and in went new valve guides. Also took the fuel tank to a radiator shop for cleaning and blew out and cleaned the fuel lines and filter assembly. A new modern fuel filter was installed in place of the original multi-leaf metal filter element.

After reassembly the jeep started instantly but would lose power and die once it warmed up. Every time. Throttle and choke no help. Everything even remotely connected with the fuel and ignition systems then got checked, rechecked, or replaced. No joy.

The fuel pump seemed to function normally when the primer lever was actuated with my fingertips over the inlet and outflow ports. The pump is from Seal Tested and has an 11/2020 date on the casing. The box that the pump came in has a notation, "suitable for use with biofuels". The pump had worked fine before the valve stuck.

Out of ideas, I replaced the pump with another new Seal Tested brand pump. The new pump primes easily and doesn't lose prime. The jeep starts instantly, runs great, and no longer dies.

Did a postmortem on the old pump and found that the diaphragm and all internals are in excellent shape. Immediately noticed though that one of the little valve springs was not properly seated in its retaining recess. The little phenolic check valve apparently did not have even spring pressure on it and could not properly seat. I believe that fuel was backflowing through that valve and that there was insufficient fuel pressure at the carb when the engine warmed up, resulting in an overly lean fuel condition.

It took a small flat blade screwdriver and about ten seconds to properly seat the spring. The pump is working fine now, and it's been moved to my spares shelf.

FWIW. Hope this experience is helpful to someone else.
Last edited by tsmgguy on Thu Feb 09, 2023 7:00 am, edited 12 times in total.
Willys MB 236426, Hood 20336549, DOD 5-20-43
Piper L-4A "Grasshopper", Sn. 10371, USAAF 43-29080, DOD 5-28-43


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Re: Seal Tested WO-A8323 Fuel Pump

Post by Frankie » Tue Feb 07, 2023 4:10 pm

Good to know!
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Re: Seal Tested WO-A8323 Fuel Pump

Post by dinof » Wed Feb 08, 2023 6:14 am

Don't feel bad, I had trouble with a rebuild kit from JMP. "O" rings instead of fiber gaskets at the check valves.

I hope JMP replaced the o rings with the proper gaskets.
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Re: Seal Tested WO-A8323 Fuel Pump

Post by tsmgguy » Fri Feb 10, 2023 7:21 am

dinof wrote:
Wed Feb 08, 2023 6:14 am
Don't feel bad, I had trouble with a rebuild kit from JMP. "O" rings instead of fiber gaskets at the check valves.

I hope JMP replaced the o rings with the proper gaskets.
Everything about this whole job went as you said it would. Thanks!
Willys MB 236426, Hood 20336549, DOD 5-20-43
Piper L-4A "Grasshopper", Sn. 10371, USAAF 43-29080, DOD 5-28-43

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Re: Seal Tested WO-A8323 Fuel Pump

Post by dinof » Fri Feb 10, 2023 8:12 am

Good to hear you got it fixed. I still worry about those rebuild kits! :?
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Re: Seal Tested WO-A8323 Fuel Pump

Post by tsmgguy » Fri Feb 10, 2023 8:29 am

Am very impressed with the quality of the Seal Tested fuel pump. I understand that Desmet is the company that makes them, and that they're located in The Netherlands. They offer a large array of parts. Bought one of their braided fuel line flex hoses and find it to be of excellent quality as well. Wouldn't be surprised to find that Desmet makes the well-regarded reproduction Carter WO JMP carb, as well.
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Re: Seal Tested WO-A8323 Fuel Pump

Post by Bangle 99 » Sat Feb 11, 2023 7:23 am

"Wouldn't be surprised to find that Desmet makes the well-regarded reproduction Carter WO JMP carb, as well."

They're 100% made in China.
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Re: Seal Tested WO-A8323 Fuel Pump

Post by tsmgguy » Sat Feb 18, 2023 7:55 am

Symptoms persist. Ran fine the other day for about 30 minutes and then quit dead, with no warning. It started again after few minutes, and I was able to drive it back to the hangar. I threw the cover over the jeep and gave up for the day.

Idle quality not great. It ran like a sewing machine before the valve guide job. Carb has been rebuilt with a master kit.

Simple stuff first. I wonder if the fuel cap vent is allowing pressure to equalize. I have an original large-mouth WWII fuel cap that's always been fine up to now. Is the vent in the cap (I assume there IS a vent) easily inspected and cleared?

Any ideas gratefully appreciated!
Willys MB 236426, Hood 20336549, DOD 5-20-43
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Re: Seal Tested WO-A8323 Fuel Pump

Post by OldGPW » Sat Feb 18, 2023 8:09 am

Hi,

what happens when you give it a little throttle? smoothes out or gets worse like the engine is going to die?

Do you have to run it with the choke out (after it warms up)?

You mentioned the carb has been rebuilt, was it rebuilt before or after you started having these problems?

At this point I wouldn't think the fuel pump is the issue but lightning can strike twice, so it can't be ruled out yet. I would first focus on the carb. The idle circuit can get plugged up pretty badly and it's tough to clear it because of how deep into the casting it is. On the other hand a bad idle could be improper fuel/air mix, or even a vacuum leak. First is to narrow down and then pinpoint the most likely cause, don't take anything apart yet.
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Re: Seal Tested WO-A8323 Fuel Pump

Post by tsmgguy » Sat Feb 18, 2023 8:37 am

OldGPW wrote:
Sat Feb 18, 2023 8:09 am
Hi,

what happens when you give it a little throttle? smoothes out or gets worse like the engine is going to die?

Do you have to run it with the choke out (after it warms up)?

You mentioned the carb has been rebuilt, was it rebuilt before or after you started having these problems?

At this point I wouldn't think the fuel pump is the issue but lightning can strike twice, so it can't be ruled out yet. I would first focus on the carb. The idle circuit can get plugged up pretty badly and it's tough to clear it because of how deep into the casting it is. On the other hand a bad idle could be improper fuel/air mix, or even a vacuum leak. First is to narrow down and then pinpoint the most likely cause, don't take anything apart yet.

Thanks!

With the engine warm when I give it a little more throttle it doesn't seem about to die. When it died it was sudden. Had some vapor locking in the distant past. Each time the fuel line flex hose had deteriorated but It's good now.

No choke or throttle needed after warm-up.

Had a load of fuel with water in it. Some rust and sediment in tank, lines, and filter. Purged this from fuel system from one end to the other. Took the tank to a radiator shop for a proper clean-out. It's spic and span inside. All fuel connections made with EZ Turn fuel lube. No leaks at the connections. No fuel smell under hood. Carb rebuilt concurrently with new valve guides, done by the very knowledgeable gent who installed the guides. He wanted to preclude any post-guide carb contamination problems. Also new distributor rotor and cap and all ignition leads, only because they were all over 20 years old. New coil, which we thought might be failing when it warmed up.

And that's about all I can think of.

On this last cold start found that the fuel pump had lost prime. Easily primed with finger lever. It never used to lose prime, regardless of how long it sat.
Last edited by tsmgguy on Sat Feb 18, 2023 2:41 pm, edited 1 time in total.
Willys MB 236426, Hood 20336549, DOD 5-20-43
Piper L-4A "Grasshopper", Sn. 10371, USAAF 43-29080, DOD 5-28-43

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Re: Seal Tested WO-A8323 Fuel Pump

Post by dinof » Sat Feb 18, 2023 12:56 pm

What worries me is that you had a valve job done on the jeep. That means you or someone had
to adjust the valves again. You say in one sentence that the idle is rough. When I was learning to
adjust the valves in my jeep, I once adjusted them too tight. It idled with a lope as in a race engine!

You also said it quit after 30 minutes of driving.....suspect to a valve adjustment too tight. After it gets
all warmed up like 30 minutes driving, could be enough to do it. Since the last thing you did to the jeep,
which was the valve adjustment after the valve job, it's worth a check.
Dino Falabrino
On the "G" since 1998.
1943 GPW 102310 DOD 3-3-43
1928 Model A Roadster Pickup
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Re: Seal Tested WO-A8323 Fuel Pump

Post by Scoutpilot » Sat Feb 18, 2023 1:36 pm

I suspect an air intrusion in the fuel line. Check all connections for tightness.
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Re: Seal Tested WO-A8323 Fuel Pump

Post by tsmgguy » Sat Feb 18, 2023 2:46 pm

Thanks much!

The valves were adjusted cold after the head went back on. This was particularly easy to do as the manifolds were off the jeep and the left front fender was removed. I'll check 'em again.

I'll remake all of the fuel connections again, too.
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Piper L-4A "Grasshopper", Sn. 10371, USAAF 43-29080, DOD 5-28-43

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Re: Seal Tested WO-A8323 Fuel Pump

Post by Adam » Sat Feb 18, 2023 2:58 pm

Just curious, Was a valve job done or were the valves just put back in? How was the valve job done? somebody come out and cut the block seats? and valves? what was done on the tappet adjusters? how are you getting the valve adjustment correct?

Troubleshoot the fuel pump,, when engine dies, look to see if the accelerator pump is pumping fuel in,,, if there is fuel there, pump most likely good.
Adam


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