Still, still, still wont start

RichJohnson · Posted: Wed Mar 23, 2011 8:35 pm Post subject: Still, still, still wont start

My darn M38a1 will not start cold. If I load it full of starting fluid it will start. Once its hot, it starts fine.
IVe verfiyed my valves and timing.

I just finished rebuiliding the carb. I did notice that one of the springs that Midwest supplied in the kit was shorter than the one that was in my carb from the last time I rebuilt it with a new clear box midwest kit. The spring was the shorter of the two diaphrams. I reused my spring because it was longer instead of the new one supplied.

Otherwise, Im totally stumped. From what I can tell, I dont think Im getting fuel to start the jeep.

Once it starts it runs and drives.
_________________
"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

MODIFIED · Member Joined: Mar 28, 2008 Posts: 353 Location: BrOoKlYn

Cacti_Ken · Posted: Wed Mar 23, 2011 9:13 pm Post subject:

Now this is interesting. My M38 has to have a few squirts of gas via the primer pump to start. I bought a rebuilt carb back when I was restoring the jeep, but I have had the carb apart back when I first installed it because it was running rich and had no adjustment.
Rebuilt or not it was dirty inside.

It performs great after it is running. Is it possible it could still run good if the springs were in wrong?
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35th Inf. Reg. "CACTI" 4th I.D. VN
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RichJohnson · Posted: Wed Mar 23, 2011 9:52 pm Post subject:

I know I got the springs in correct, I had the parts laid out as I did it. All I did was reuse my old pump spring because it was a bit longer and stronger than the new one supplied in the kit. I was surprised at that.

Would any of that have anything to do with starting any way?

Once started it drives fine.

Just feels like Im not getting any fuel on cranking. No puff no fire at all.
_________________
"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

wesk · Posted: Wed Mar 23, 2011 11:09 pm Post subject:

Cold starting a YS carb requires the choke full closed. The reason for this is not what you think it is. For the engine to develop adequate vacuum when cranking to operate the accelerator pump it must be closed.

Poor cold starting when cranking her with the choke fully closed is indicative of two possible problems. One the bowl is empty. Two the accelerator pump is not working.

The wrong spring or an incorrectly installed spring in the accelerator pump diaphragm can give you a lot of grief. The spring's position is shown incorrectly in the TM on the carb.

Make sure you have it this way:

If the bowl is empty when you are trying to start her cold then use the hand pump lever on the fuel pump to fill the bowl before you try to start her.

Finally a very rare issue can be with a manifold crack or warping that is worse when she's cold and seals better when she is warm.
_________________
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

RichJohnson · Posted: Thu Mar 24, 2011 8:52 am Post subject:

Wes, Im betting that somehow its got to be in the pump spring issue.
Like I said, the kit I got had a shorter spring than what was in my carb. Which is strange since they were both midwest mil clear box kits.
What is the correct length of the spring for the pump diaphram.

I will pull my carb, go through it again, and compare lengths of the spring in the carb to the spring still in the box that I did not use if someone can post the correct length of it.

My fuel pump has the handle, but for some reason it does not pump. I think the shaft is snapped off inside or something.
_________________
"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

wesk · Posted: Thu Mar 24, 2011 9:54 am Post subject:

While you are in there check for the correct metering rod and metering rod spring.
[img]http://img.mypicgallery.com/Default.aspx?/willysmc/metering-rod-dimensions.jpg&d=0&t=3%2f24%2f2011+11%3a44%3a58+AM[/img]

[img]http://img.mypicgallery.com/Default.aspx?/mcfuelsystem/midwest-kit-labeled.jpg&d=0&t=3%2f24%2f2011+11%3a47%3a46+AM[/img]

I have a drawing somewhere with spring dimensions but the key is the accelerator pump gets the beefier spring.

Have you checked fuel pump output pressure yet? That broken manual pump handle may be part of a bigger problem.

Have you positively confirmed the fuel bowl level prior to starting cold?
_________________
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

RichJohnson · Posted: Thu Mar 24, 2011 8:38 pm Post subject:

Those pics did not show up Wes.

How would I check the fuel bowl level before starting?

So Im now confused on the springs. Which side gets the longer spring? Pump side or metering rod side.

I would really like it if somebody could post the length of the springs. I want to compare it to the length of the springs I reused compared to the different length one I left in the new kit.

Tonight I started it up and ran it for a while. The idle speed goes all over the place on its own. Im wondering if you didnt steer into something by bringing up the pump.

Is it possible to have enough pressure to run and drive, yet not generate enough while cranking to get it to start?
_________________
"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

wesk · Posted: Thu Mar 24, 2011 11:30 pm Post subject:

To check the fuel level in the bowl remove the 6 screws that hold the air horn on top of the bowl and lift the air horn enough to see the fuel level.

Although the M38 and the M38A1 use the same metering rod spring they do not use the same accelerator pump spring. The illustration above will give you the dimensions you seek.

A wandering idle is usually caused by a worn throttle shaft and/or the two bushings. A very low or fluctuating fuel level in the bowel can cause the wander as well. Try a propane enrichment test paying particular attention to the throttle shaft bushings. Cracked carb bodies can also cause the issue.

As I mentioned above you really need to establish a few things positively before you start shooting in the dark.

1-Cleanliness. Carb, fuel pump, plumbing and tank. Any moving trash can give you the grief you are experiencing.

2-Fuel pump delivery pressure.

3-Float level setting and actual fuel level in the bowel.
_________________
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

RichJohnson · Posted: Sat Mar 26, 2011 6:28 pm Post subject:

Loosened up the top of the carb so I could see inside. I have not cranked the jeep in almost 2 days. The bowl was empty. I put it back on and cranked it over and then took it off again and the bowl was about 1/3 full.

How does that sound?

I was pretty carefull setting my float level, does it sound like I got it wrong?
_________________
"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

wesk · Posted: Sat Mar 26, 2011 8:12 pm Post subject:

Sounds about right. You should now see why the fuel pump is suppose to have a hand pumping lever. She won't start properly until the bowl is full, the accelerator is charged and the choke is full closed.

To verify the float setting snug the air horn screws and start the jeep. Then shut down and immediately pop the air horn loose and see where the fuel level is.
_________________
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

RichJohnson · Posted: Sun Apr 03, 2011 12:44 pm Post subject:

Just started the jeep. Warmed it up and drove it around the block. Parked it and pulled the top off the carb. The fule level is about half full, give or take. I took some pictures of it up super close if need be but didnt upload them on the net yet.

Does that mean my float level is too tight, not letting the bowl fill up enough?
_________________
"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

wesk · Posted: Sun Apr 03, 2011 9:25 pm Post subject:

Give or take is not quite accurate enough.

Measurement #1 - Invert the air horn and measure the distance from the gasket surface to the bottom (lowermost) edge of the float.
Measurement #2 - Now measure the distance from the top mating surface of the bowl to the top of the fuel in the bowl.

#2 should be about 1/4" less than measurement @1. Give or take! If she's close to this measurement it only means that wherever the float is set the fuel is getting to that height.

The correct float setting is in the spec sheet and is measured between the top of the float and the gasket surface of the air horn.
_________________
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

RichJohnson · Posted: Sun Apr 03, 2011 11:22 pm Post subject:

Yeah, the manual for the carb says I think from memory 1/4 inch for the float setting without the gasket in the way.
I think this is my problem. The fuel looked too low. It was about middle of the bowl.

If it aint then I will keep looking. Next change I get that carb is comming off again. I will measure and reset the float if need be.
I will also remove and measure the springs on both sides to pin that issue down.

If that dont turn out to be it then I will look to the fuel pump.
_________________
"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

RichJohnson · Posted: Sun May 01, 2011 1:44 pm Post subject:

Well, I've finally got the carb on the bench and have it torn back apart.

I have mic'ed the springs that were in the carb and they come to this
Accelerator pump -.630
Metering rod - 1.260

So basically, Midwestmil sent me the wrong kit. I thought somthing was up when I noticed that the kit included the check ball and weight for the m38 carb. I kind of assumed that maybe he made a one composit kit to do both but maybe he just sent me an m38 kit as apposed to an m38a1 kit. Funny though, all the gaskets fit right. Not sure if the gaskets are interchangeable or not. between the 650 and 950.

I mic'ed the metering rod and it specs out so I guess Im fine there.

I pulled my old springs out of the box and checked them, they are spot on to your diagram so I am going to reuse them.

I am going to have pollite words with John about this. The box just says carter carb kit.

Any futher suggestions?
I am going to go have lunch and then put it back together and see if I can get the jeep to start. Will follow up tonight.
_________________
"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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