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willysmjeeps.com :: View topic - M38a1 carb leaking fuel from top screws
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M38a1 carb leaking fuel from top screws
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RichJohnson
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Joined: Apr 15, 2005
Posts: 162
Location: San Diego CA

PostPosted: Sat Oct 23, 2021 5:59 pm    Post subject: M38a1 carb leaking fuel from top screws Reply with quote

I rebuilt the stock M38a1 carb with a kit from midwest and fuel keeps coming out the top from the throttle cable bracket screws and the 1 screw forward of them on the forward side of the fuel inlet line.

I have verified my float setting per the manual and I just cant figure why this is happening.

Is it a faulty gasket?

Is there too much fuel pressure, it has a new autozone CJ fuel pump but it ran ok before I rebuit it....

Opinions on what to do next.

I had it running good for a bit today then it just clogged up and doesnt want to idle, or start or even drive. the high speed circuit just dropped off entirely. It must have clogged up for all this to happen, Ive rebuilt several of these carbs over the years so Im pretty good at it and yet this one has me stumped.
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KI6EZA
1954 M38A1 (first civilain owner)
1965 M37B1 Commo shelter truck
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wesk
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Location: Wisconsin

PostPosted: Sat Oct 23, 2021 11:28 pm    Post subject: Reply with quote

Two quick checks come to mind.

1 - Remove the top section (air Horn) after you are sure the bowl has filled up and confirm the inlet needle is firmly seated and not allowing any more fuel in.

2 - With a pressure gage T'd into the line from the fuel pump to the carb check the actual output pressure of the pump.

Looking at my illustration below which # screws are leaking?


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Wes K
45 MB, 51 M38, 54 M37, 66 M101A1, 60 CJ5, 76 DJ5D, 47Bantam T3-C & 5? M100

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RichJohnson
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Posts: 162
Location: San Diego CA

PostPosted: Sun Oct 24, 2021 12:11 pm    Post subject: Reply with quote

Screws # 1,2 and 6 are leaking. I dry them, then you can see a film slowly develop and then a puddle.

The only needle I am aware of is the one above the float right?
Once I lift the air horn off the bowl the float will droop and the needle will open all the way simulating an empty bowl.

I know that when I set the float level, and then reset it again per the manual, the float was sitting on the spring of the needle, which I read is how it should be gauged if I was correct. The float could have been pushed down on the air horn further compressing the spring (while air horn is inverted of course)

Im not aware of how to perform the needle test you suggest.

I will look into how to test the fuel pressure. have no idea currently. Google and youtube academy should help.
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"Those who enjoy freedom must endeavor to preserve it"

KI6EZA
1954 M38A1 (first civilain owner)
1965 M37B1 Commo shelter truck
MBT
GRC-122 TTY rig
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wesk
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PostPosted: Tue Oct 26, 2021 1:56 am    Post subject: Reply with quote

To leak from the screws the carb bowl has to be overfilling.
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Wes K
45 MB, 51 M38, 54 M37, 66 M101A1, 60 CJ5, 76 DJ5D, 47Bantam T3-C & 5? M100

Mjeeps photo album: http://www.willysmjeeps.com/v2/modules.php?set_albumName=Wes-Knettle&op=modload&name=gallery&file=index&include=view_album.php
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Yarder
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Joined: Feb 18, 2009
Posts: 43
Location: Seattle, WA USA

PostPosted: Fri Oct 29, 2021 8:44 pm    Post subject: Reply with quote

I had an issue just like that. I had set my float, etc. Turns out that my float wasn't correctly floating. It had, over the years, gotten fuel inside it. I followed the book to put the float in a pan of hot water, watch at the bubbles came out, and noted the location. Then removed the float and sanded the area, and soldered the leaking spot.
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RichJohnson
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Location: San Diego CA

PostPosted: Sat Oct 30, 2021 10:33 am    Post subject: Reply with quote

Ok, I will look for a leak in the float.

I guess other problem could be the pump is too much pressure and pushing past the float needle since the float is set properly.
I still need to get a fuel pressure test done.
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"Those who enjoy freedom must endeavor to preserve it"

KI6EZA
1954 M38A1 (first civilain owner)
1965 M37B1 Commo shelter truck
MBT
GRC-122 TTY rig
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RichJohnson
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Joined: Apr 15, 2005
Posts: 162
Location: San Diego CA

PostPosted: Mon Feb 14, 2022 6:51 pm    Post subject: Reply with quote

Well I am still ripping my hair out with this problem.
I have worked on it all day again.

I took the carb off and went all through it and double checked the float setting to 1/4 inch spec and put the float in near boiling water to check for leaks. Both are good. The carb was nice and clean still on the inside.

I tried to get a pressure reading from the pump with a vaccuum / fuel gauge and it showed 3 psi. I kinda doubted that was accurate because its an old chinese gauge.

So I just put a generic fuel pressure regulator on it after the filter in front of the carb and set it for 4 psi.

Fuel still leaks out of the top of the screws on the top of the carb.
I lowered it to 3 psi and still the #@$%@ fuel leaks out of the top of the carb and it start to flood the engine out.

While I had the carb apart I checked that the needle and seat were closing and gently pushed on them and blew into the fuel inlet and my airflow was stopped.

What do I do now?[/img]
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"Those who enjoy freedom must endeavor to preserve it"

KI6EZA
1954 M38A1 (first civilain owner)
1965 M37B1 Commo shelter truck
MBT
GRC-122 TTY rig
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wesk
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PostPosted: Mon Feb 14, 2022 8:50 pm    Post subject: Reply with quote

Swap the carb for a known good one. Doesn't have to be a YS. It can be a YF or a Solex as well. Check your MVPA membership for a MV owner close to you who may have a carb to loan.

If the problem goes away then you have a lot of re-inspecting and a serious inventory of your carb parts. You might also consider sending your carb to an experienced professional rebuilder.

If the problem remains with the substitute carb then you are back to fuel pump pressure & manifold vacuum issues.
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Wes K
45 MB, 51 M38, 54 M37, 66 M101A1, 60 CJ5, 76 DJ5D, 47Bantam T3-C & 5? M100

Mjeeps photo album: http://www.willysmjeeps.com/v2/modules.php?set_albumName=Wes-Knettle&op=modload&name=gallery&file=index&include=view_album.php
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RichJohnson
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PostPosted: Mon Feb 21, 2022 2:37 pm    Post subject: Reply with quote

I opened my carb up again and compared the needle and seat and float spring to unused ones from Midwest Military supplied kits along with a very old take out that I saved. Springs are marked


I also compared the entire aparatus
left is existing problematic one in my NASA jeep, right is new MM kit



Ok well I cant get the photos to work.
But since the springs are all different heights and tensions the manual setting of 1/4 float from bowl lid must mean nothing now a days with the variance in parts.
So is it just a trial and error until you get the tab on the float with enough tension?
_________________
"Those who enjoy freedom must endeavor to preserve it"

KI6EZA
1954 M38A1 (first civilain owner)
1965 M37B1 Commo shelter truck
MBT
GRC-122 TTY rig


Last edited by RichJohnson on Mon Feb 21, 2022 4:22 pm; edited 1 time in total
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RonD2
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Joined: Oct 02, 2014
Posts: 1887
Location: South Carolina, Dorchester County

PostPosted: Mon Feb 21, 2022 3:17 pm    Post subject: Reply with quote

Hi Rich,
You can't use the [img} and [img/] unless your photos are loaded to your photo album on this site.
They won't work if you store them anywhere else.

Good luck!
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Ron D.
1951 M38 Unknown Serial Number
1951 M100 Dunbar Kapple 01169903 dod 5-51

“The only good sports car that America ever made was the Jeep."
--- Enzo Ferrari

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RichJohnson
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Location: San Diego CA

PostPosted: Mon Feb 21, 2022 3:27 pm    Post subject: Reply with quote

Ok so I installed the first MM kit needle and seat and cannot lower the tab enough for gas to come out of the fuel line while holding the horn connected to the fuel line and cranking the motor. So that spring is just too tight, I have the tab flat all the way basically non exsistant.
So the supplied springs in those kits are just not going to work as both that were new and never used as shown in my photo are about the same height.

I put the needle seat spring back in that I was having trouble with the flooding out and bent the tab back up but did not set the float at 1/4 inch per the manual since that was allowing the flooding to happen. I gave it about a 3/8 setting give or take and connected it to the horn to the fuel line and cranked the motor. I get fuel squirting while the float is drooped and the fuel shuts off at about half of the swing of the float.

Since this seems to have degraded to a trial and error setting process, does anyone know what position the float is supposed to be in when the fuel shuts off? That would give me an accurate target to shoot for setting up since the inverted float to bowl lid of 1/4 inch is totally inadequate for the parts available.

I have rebuilt these carbs, 650 and 950 style at least 8 times so far between my other jeeps and friends jeeps and this is the first time I have had so much trouble. I usually dont replace the hard brass parts if they are clean and not worn. Its just our California gas seems to eat the diaphrams in about 2-3 years.
_________________
"Those who enjoy freedom must endeavor to preserve it"

KI6EZA
1954 M38A1 (first civilain owner)
1965 M37B1 Commo shelter truck
MBT
GRC-122 TTY rig
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BobW
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Location: Monticello, NY

PostPosted: Mon Feb 21, 2022 6:42 pm    Post subject: Reply with quote





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Bob W. Monticello, NY. 1952 CJ3A, 1952 M38, 1950 CJV-35/U
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wesk
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PostPosted: Mon Feb 21, 2022 9:13 pm    Post subject: Reply with quote

RonD said:

Quote:
Hi Rich,
You can't use the [img} and [img/] unless your photos are loaded to your photo album on this site.
They won't work if you store them anywhere else.


The [img][/img] brackets work fine with other photo storage sites so long as you file them in a public file (one that does require the viewer to log in). As you can see Bob W accessed them and I also accessed them and used the correct "Login free" link inside the [img][/img] brackets.

[/quote]
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Wes K
45 MB, 51 M38, 54 M37, 66 M101A1, 60 CJ5, 76 DJ5D, 47Bantam T3-C & 5? M100

Mjeeps photo album: http://www.willysmjeeps.com/v2/modules.php?set_albumName=Wes-Knettle&op=modload&name=gallery&file=index&include=view_album.php


Last edited by wesk on Mon Feb 21, 2022 10:28 pm; edited 1 time in total
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RichJohnson
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Posts: 162
Location: San Diego CA

PostPosted: Mon Feb 21, 2022 9:28 pm    Post subject: Reply with quote

Hunh, I didnt know one had to log in to flicker to see pictures. I have viewed others without being logged in I know, because I have to log in when I want to go to my stuff. Obviously there is a public link and I didnt know and didnt find it. I just clicked on the share photo and it gave me a link to share.


Well with the carb.... I started up the jeep with the existing needle and seat set to a bit more than 3/8 it turned out and then ran it for a while making some adjustments and throttling it up and got it warmed up. I didnt get a chance to drive it.
I shut her down and pulled the air horn cover and the bowl was a bit low by my own judgement guess so I readjusted the float a little closer to the lid while inverted. Much closer to 3/8 or less clearance and put it all back together and gave it a go.
She fired up and ran and never flooded or leaked fuel like she used to.
I didnt get to drive it so Im going to leave it set up the way it is right now till I get a chance to drive it around.

Those springs that came in the new rebuild kits are so stiff and tall that the float cannot be adjusted to allow fuel to enter the bowl at all.
One is going to have to start cutting the springs down to make adjustments by guestimation and testing like I did rather than by the manual since the parts are not exactly milspec.

Wes, do you have a needle seat and spring that is known take out that is true milspec that you could show us how far the spring pin should stick out from the needle?

Its too bad the springs in the kits just will not work as supplied and modification is necessary.

Hopefully now that I have gone through all this headache anybody else that experiences flooding after a carb rebuild with a new kit can address the float needle spring and tab setting by trial and error.
_________________
"Those who enjoy freedom must endeavor to preserve it"

KI6EZA
1954 M38A1 (first civilain owner)
1965 M37B1 Commo shelter truck
MBT
GRC-122 TTY rig
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wesk
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Posts: 16225
Location: Wisconsin

PostPosted: Tue Feb 22, 2022 12:45 am    Post subject: Reply with quote

Quote:
Wes, do you have a needle seat and spring that is known take out that is true milspec that you could show us how far the spring pin should stick out from the needle?

Its too bad the springs in the kits just will not work as supplied and modification is necessary.



Spring is 1.5 coils longer than the plunger

Here's John's Kit:



Here's Ron F's kit:



compare the needle pluger height between the two kits.
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Wes K
45 MB, 51 M38, 54 M37, 66 M101A1, 60 CJ5, 76 DJ5D, 47Bantam T3-C & 5? M100

Mjeeps photo album: http://www.willysmjeeps.com/v2/modules.php?set_albumName=Wes-Knettle&op=modload&name=gallery&file=index&include=view_album.php
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