M38a1 carb leaking fuel from top screws

RichJohnson · Post by **RichJohnson** » Sat Oct 23, 2021 5:59 pm

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.

Post by **wesk** » Sat Oct 23, 2021 11:28 pm

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?

RichJohnson · Post by **RichJohnson** » Sun Oct 24, 2021 12:11 pm

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.

Post by **wesk** » Tue Oct 26, 2021 1:56 am

To leak from the screws the carb bowl has to be overfilling.

Yarder · Post by **Yarder** » Fri Oct 29, 2021 8:44 pm

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.

RichJohnson · Post by **RichJohnson** » Sat Oct 30, 2021 10:33 am

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.

RichJohnson · Post by **RichJohnson** » Mon Feb 14, 2022 6:51 pm

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]

Post by **wesk** » Mon Feb 14, 2022 8:50 pm

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.

RichJohnson · Post by **RichJohnson** » Mon Feb 21, 2022 2:37 pm

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?

RonD2 · Post by **RonD2** » Mon Feb 21, 2022 3:17 pm

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!

RichJohnson · Post by **RichJohnson** » Mon Feb 21, 2022 3:27 pm

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.

BobW · Post by **BobW** » Mon Feb 21, 2022 6:42 pm

Post by **wesk** » Mon Feb 21, 2022 9:13 pm

RonD said:

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

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

brackets.

[/quote]

RichJohnson · Post by **RichJohnson** » Mon Feb 21, 2022 9:28 pm

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.

Post by **wesk** » Tue Feb 22, 2022 12:45 am

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.