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Fuel pump difference

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Willy Nilly View Drop Down
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    Posted: 05 Oct. 2022 at 11:26pm
The metal cover fuel pump on the right came off my running L134 engine. The glass bowl fuel pump on the left was in my spare parts bin.  Notice the big difference in the lever position.  Both levers rise to approximately the same height.  Is one pump right and one wrong?

Also there was no spacer on my pump. but I have one that I think I will put on.  Should I?


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Post Options Post Options   Thanks (1) Thanks(1)   Quote Oldpappy Quote  Post ReplyReply Direct Link To This Post Posted: 06 Oct. 2022 at 6:02am
The pumps were made by several different companies. I prefer the glass bowl "AC" type on the left.

The spacer is used to reduce fuel pressure which to match the specs for certain carburetors. 

If you have a Carter WO carburetor you do not need the spacer. If you have a SOLEX you may, or may not need it. 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote General Eisenhower Quote  Post ReplyReply Direct Link To This Post Posted: 06 Oct. 2022 at 8:18am
I've always been curious as to the metal top one, as I have one as well.
However I do prefer the glass bowl type, I like to visually see fuel movement
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Lee MN View Drop Down
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Post Options Post Options   Thanks (1) Thanks(1)   Quote Lee MN Quote  Post ReplyReply Direct Link To This Post Posted: 06 Oct. 2022 at 11:37am
It would make no difference where the lever is positioned off the engine, the camshaft will determine where the lever position is when mounted on the engine, so both pumps would be exactly the same mounted on the engine.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote Joe Friday Quote  Post ReplyReply Direct Link To This Post Posted: 06 Oct. 2022 at 11:57am
Without the casting numbers and maybe the date code on the other side of the base casting I can't be sure.

I prefer the glass bowl AC.

What is the brand of the one on the right?
It looks a little like the current airtex pumps. I bought out the remaining 'closeout ' (non-returnable) stock from Rock Auto cheap, just to find out they didn't work. I apparently pitched all but one of them, and discovered they needed to be used with an 1/8 spacer. Now my metal topped Airtex works fine. 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Willy Nilly Quote  Post ReplyReply Direct Link To This Post Posted: 06 Oct. 2022 at 12:45pm
I don't see any brand name or casting numbers on either pump.  But I had been running the metal top fuel pump without a spacer, with a Solex carburetor without any issue.
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Post Options Post Options   Thanks (1) Thanks(1)   Quote Oldpappy Quote  Post ReplyReply Direct Link To This Post Posted: 06 Oct. 2022 at 1:02pm
So, why did you take it off?

Never mind, I see from your thread about pistons that you are rebuilding the engine, which answers the above question.

The reproduction pumps with the divided glass bowl on top are not very good, or at least the one I bought wasn't. 

I run only non-ethanol fuel in my Jeeps, but even so the diaphragm and seal on the reproduction pump I had on my CJ2A began to leak after a few months.

I don't know if any of the new pumps available now are any better, so I just rebuilt an original AC with a quality kit with diaphragm and seals that hold up to modern fuels.

I have a reproduction dual action pump on my CJ5 which I bought from QTM. It has been on the Jeep for about a year and a half without any indication of leaking, but if it doesn't last I will again rebuild an original.

I have a new pump that looks like the one you have with the metal top. I bought it from Rock Auto a couple years ago and it was listed as being a "Carter", but I don't know if it really is. 




Edited by Oldpappy - 06 Oct. 2022 at 1:15pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Bruce W Quote  Post ReplyReply Direct Link To This Post Posted: 06 Oct. 2022 at 2:17pm
  AFAIK, no spacers were used with any “single-action” fuel pumps from Willys. They were only used with the “double- (or dual-) action (fuel and vacuum) pumps. 
  I need to do some testing, but I don’t believe the spacer will reduce pressure. It will alter the geometrical relation of the pump lever, the camshaft, the pivot point, and the connection to the diaphragm. This will change the amount of fuel per stroke, or volume. Pressure is produced and controlled, not by the pump arm action, but by the diaphragm spring. Only if volume is reduced to the point where the carburetor delivers more fuel than the pump can supply will pressure be reduced. If anyone can produce facts pertaining to fluid flow and pressure or test results, showing that I’m wrong, I would be interested and even glad to see them. 
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Post Options Post Options   Thanks (1) Thanks(1)   Quote Bill Norris Quote  Post ReplyReply Direct Link To This Post Posted: 06 Oct. 2022 at 2:33pm
Not sure if this helps or confuses, but Walcks says the spacer is required for all:

I’ve been having issues with my carb flooding. Checked the float level, tried different needles and seats and still floods. I am going to try one of their spacers to see if it makes a difference. 

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Post Options Post Options   Thanks (0) Thanks(0)   Quote Oldpappy Quote  Post ReplyReply Direct Link To This Post Posted: 06 Oct. 2022 at 3:07pm
I have only seen the spacers with the dual action pumps, and found one on a M38A1 in a junk yard once but there was no pump on that engine so I don't know what it had.

Hadn't thought about it as much as Bruce evidently has, and heard somewhere the spacer was to reduce pressure, now I don't know what it is for. 
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Post Options Post Options   Thanks (1) Thanks(1)   Quote Ron D Quote  Post ReplyReply Direct Link To This Post Posted: 06 Oct. 2022 at 3:22pm
The military dual-action fuel pumps used on the M38 and M38A1 use an unmistakably thick 5/8-inch spacer to regulate correct fuel pressure from the pump.

I believe the CJ dual-action pumps use a 1/8-inch spacer for the same reason.

If you aren't sure you need one or not, you could look up the correct fuel pressure for what you have in the manual, install the pump with a spacer and then without it, measuring the pump pressure with a gauge for each instance. Not using a pressure gauge is just guessing.

If I remember my 8th grade geometry correctly, lengthening a lever (with a spacer), would serve to reduce movement on the little end, which I'd think would reduce output pressure.

Gaskets are cheap. Spacers take 2.

Good luck!


Edited by Ron D - 06 Oct. 2022 at 3:34pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Joe Friday Quote  Post ReplyReply Direct Link To This Post Posted: 06 Oct. 2022 at 3:28pm
I just picked up a half dozen NOS 1/8 spacers 2 weeks ago, and now I can't find them.

FWIW it is not listed in the CJ2A Bill of Materials, but the 639183 part number tells me it was MB or earlier, so maybe I need to search more.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Bruce W Quote  Post ReplyReply Direct Link To This Post Posted: 06 Oct. 2022 at 3:40pm
  Let us know how it comes out, Bill. If you could run a pressure test and volume test before and after it would help us. 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Bill Norris Quote  Post ReplyReply Direct Link To This Post Posted: 06 Oct. 2022 at 3:54pm
Just to clarify I have a glass bowl pump that I got from Walcks maybe 5-6 years ago. I’ll see if I have something to test the pressure with. 

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Post Options Post Options   Thanks (1) Thanks(1)   Quote oldtime Quote  Post ReplyReply Direct Link To This Post Posted: 06 Oct. 2022 at 3:58pm
I did a post on this exact topic over the old 3B bulletin board many years ago. Basically the spacer effects pump volume only and that’s because it effects the throw distance of the pump arm. 
They were used on AC 4693 dual action pumps because these engines don’t require near as much fuel as the pump will supply.
In case you never realized it the Willys 134 pumps are all mounted upside down. 
The pumps were designed by AC to fit most standard applications. Not the upside down Willys.
The glass bowls were actually intended to be visual sediment bowls not domes.


Edited by oldtime - 06 Oct. 2022 at 4:07pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Oldpappy Quote  Post ReplyReply Direct Link To This Post Posted: 06 Oct. 2022 at 6:02pm
Thanks Ken,

Interesting about the glass bowl pump. I always wondered why it was on top in a Jeep, but on bottom in every other vehicle I have ever seen with a glass bowl pump, including the old Ford tractors I have owned, and other cars and trucks I have owned or worked on.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Ron D Quote  Post ReplyReply Direct Link To This Post Posted: 06 Oct. 2022 at 8:03pm
Originally posted by oldtime oldtime wrote:

Basically the spacer effects pump volume only and that’s because it effects the throw distance of the pump arm.

If the spacer effects only volume, that would seem to indicate that only the cam lobe spinning is what makes pressure (more RPM's = more pressure, less RPM's = less pressure)?

I think the relationship between volume and pressure might be more complicated than that?

What happens to volume and pressure when the carb float valve closes (yes, momentarily) because the bowl is full?
Obviously volume goes to zero and pressure remains dependent on how many RPM's the cam lobe spins?

I'd like to read your old write up on pump operation.
Straighten me out.
Can you point us to it?

Thanks!





Edited by Ron D - 06 Oct. 2022 at 8:04pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Bill Norris Quote  Post ReplyReply Direct Link To This Post Posted: 06 Oct. 2022 at 8:25pm
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