Posted: Wed Aug 09, 2017 6:31 am Post subject: M38a1 Idle Issues
I have a 1953 M38a1 with a YS Carburetor.
It has trouble idling, but only after running it as high RPM's for an extended amount of time. When I go out and start it for the first time that day, it will sit there and idle all day(it does have a little rough idle).
I just rebuilt the Carburetor with a kit, and the needle it came with was longer than the one that's in it. When I set the float to 1/4" with the needle that's in it, it floods bad. When I tried to put the new(longer) needle in it, I couldn't even get it to adjust to 1/4" with adjusting the metal tab. How should the needle sit in its seat? Should the bottom of it be flush or should it stick out some? I want to make sure I'm using the correct needle.
I'd like to add that I adjusted the original needle to a larger gap than 1/4" and that's where it is now.
Last edited by UncleSam on Wed Aug 09, 2017 10:18 am; edited 1 time in total
There is no substitution of parts that will work. Who's kit are you using?
Are you following the TM we have loaded to our web site?
http://www.willysmjeeps.com/v2/modules.php?name=Downloads&d_op=getit&lid=142
This manaul was based on the M38's carb YS637S. Differences with the m38A1 carb YS950S are minimal and are explained well enough in the M38A1 parts manual and the attached YS950S spec sheets. Be care when using the TM 9-1826A page 114 fig 60 shows the metering rod spring item BB on the wrong side of the vacuum diaphragm. I have posted a corrected fig 60.
One difference between needles is that the one in it now has a rubber tip and is shorter, the new one is solid brass(I guess) and is a little longer.
Something I noticed when I looked a the TM was the "Tube for balanced venting" is just plugged on my carburetor. Is it essential to have this tube from the air horn to the air cleaner?
I did follow the directions correctly for setting the float, but it floods terrible when I set it to a 1/4". I don't think the extra 64th would make a huge difference, but I could try it. Maybe the float itself is bent and not the tab?
Also, if I set the idle adjustment screw to 1 turn open, it won't idle. I have it open at least a couple turns right now.
Thanks for the help, this site is pretty amazing. I joined it because I have been pretty stomped with this issue. I'm surprised there are people who help and ask nothing in return.
Joined: Aug 31, 2010 Posts: 1751 Location: SO IDAHO
Posted: Wed Aug 09, 2017 12:30 pm Post subject:
UncleSam wrote:
Something I noticed when I looked a the TM was the "Tube for balanced venting" is just plugged on my carburetor. Is it essential to have this tube from the air horn to the air cleaner?
.
Sam, the YS carb by nature is closed to atmosphere. The fuel bowl MUST be vented, that's where the tube comes in. That one observation may be cause for much of your carburetion problem. _________________ keep 'em rollin'
RICKG MC 51986 DOD 01-52, '50 CJ3a
Still working on this issue...
I added the hose, I have the float set correctly now, and I added a fuel pressure regulator(set on 2). I also changed a fuel filter that was clogged. It overall runs better now, but I still have 1 issue.
If I'm holding high RPM's for a minute and abruptly let off the throttle, it dies. If I keep it running, it will run poorly for a while before it's able to idle again on its on. The next thing I was going to replace was the ignition coil. Any thoughts would be appreciated!
You mention a pressure regulator? Do you have an electric fuel pump?
How did you sort out the float needle & seat issue? I posted two very clear photos above the needle & seat laying out with the kit and the next photo shows it clearly installed. Have you got a needle & seat to match my illustrations yet?
Have you confirmed all parts in your carb are the exact parts that belong in it?
Make sure this ball is not missing.
If your tank has the fording cap installed make sure the vent is open.
If you have the fording valves on your jeep make sure they are not in the fording position. _________________ Wes K
45 MB, 51 M38, 54 M37, 66 M101A1, 60 CJ5, 76 DJ5D, 47Bantam T3-C & 5? M100
1) Changing the ignition coil didn't help, I read that they may fail when they get hot.
2) I do have an electronic fuel pump, so I added a fuel pressure regulator and currently have it set to 2.
3) I think adding that vent hose on carb may have let me set the float correctly, I'm not entirely sure.
4) Those pictures should be very helpful, I just bought a digital caliper, so when I get a minute I will go through the pieces and measure them. I am concerned I bought a cheap rebuild kit.
There are only two good kits out there. Midwest Military/Army Jeep Parts and Ron Fitzpatrick Jeep parts. The rest are offshore or ancient NOS units.
Save your money and troubleshoot by steps and in good detail. Coils are easily checked with a coil checker and you should have someone near you that has one. You can determine their health on your own with a good quality digital VOM. Use one to measure primary and secondary resistance on the coil while it is cold and then again while it is warm. You can warm it with any heat gun or hair dryer until it is slightly uncomfortable to hold.
Make sure points are open during the test if you do not disconnect the B or D terminal. Also remove the screw-on outside wire connector or disconnect A term during tests.
All the external troubleshooting you are doing on the carb may be for naught since you have NOT confirmed the parts you installed in it are in fact the correct parts. _________________ Wes K
45 MB, 51 M38, 54 M37, 66 M101A1, 60 CJ5, 76 DJ5D, 47Bantam T3-C & 5? M100
Neither the old or new metering rod measurements were exact. The one I took out read "75-595s" which I think is wrong for a M38A1?
I tried to verify that my carb is a YS-950S.
The markings on it include:
Carter YS
0-818
1-897
Patent #2048536 2328804
I really want to buy a quality rebuild kit and redo it, but I don't want to waste more money if that isn't the issue.
Also I installed a fuel pressure gauge right before my carb to test my regulator and they are both working, the pressure doesn't help or hurt this issue.
Your carb is a YS950S but I wonder why you only have 2 of the later patent #'s on yours.
Quote:
The one I took out read "75-595s" which I think is wrong for a M38A1?
Have you reviewed your ORD 9 SNL G-758 page 79 Rod, ORD PN 8329832 & Carter PN 75-826S?
75-595s is for the smaller M38 carb the YS637S.
I must emphasize what I have already mentioned. Your carb needs a complete teardown and re-accomplish the correct rebuild steps for a YS950S insuring only the correct parts are used & adhering to the YS950S spec sheet.
Also you did not tell us exactly what pressure your electric pump is putting out. The correct pressure is 4 1/2 to 5 PSI at 1800 RPM. This is found on page 144 of your TM 9-8014.
You should also check vacuum with engine operating per the same manual on pages 103-105. _________________ Wes K
45 MB, 51 M38, 54 M37, 66 M101A1, 60 CJ5, 76 DJ5D, 47Bantam T3-C & 5? M100
I APPRECIATE ALL OF YOUR HELP!
I'm pretty sure it's running good now, at least all last night I drove it around with no problems. The only issue is that I changed a couple things, so I'm not 100% on what exactly fixed it.
1st - I removed the carb and valve cover plates to adjust the lash in the intake and exhaust valves.
- The intake valves required minimal adjustment while the exhaust valves were way to tight. (Could explain it running good cold, but not hot)
2nd - Previously I had switched back to the metering rod that was originally in it, but I realized I didn't switch the "female" piece that the metering goes into, so I installed the old one back in it.
3rd - I took the time to get the float set to exactly 5/16", but now I see that that isn't the correct measurement.
4th - Gasket was slightly covering hole, so I cut it out of the way. (Pic)
I regret not buying a quality rebuilt kit. I would have saved a lot of time diagnosing this or may not have had any issues to start with.
If your curious about the outcome I can try to answer questions.
As of now, I have my Fuel PSI at 2, it doesn't seem to starve for fuel. I may turn it up to 3 or 4 and see if it makes any difference.
I am going to reset my float to 9/64" and see how that does also.
If neither of your metering rods match the dimensions of the M38A1 rod then neither of your metering rods are correct. You really need to get the correct 75-826S metering rod!
Post the measurements of that new rounded rod. _________________ Wes K
45 MB, 51 M38, 54 M37, 66 M101A1, 60 CJ5, 76 DJ5D, 47Bantam T3-C & 5? M100
You cannot post new topics in this forum You cannot reply to topics in this forum You cannot edit your posts in this forum You cannot delete your posts in this forum You cannot vote in polls in this forum
Forum FAQ
Search
Usergroups
Profile
Log in to check your private messages
Log in
