Create an account Home  ·  ·  Forums  ·  ·  Articles  ·  ·  Downloads  ·  ·  Photo Gallery  
Login
Nickname

Password

Don't have an account yet? You can create one here.

Navigation
· Home
· Article Archive
· Article Submit
· Downloads
· FAQ
· Forums
· Members List
· Photo Gallery
· Private Messages
· Web Links
· Your Account

Search Articles



Forums

Wiper motor...which is the correct one?
Lead additive, one more question.
M31C mount with or without replica weapon
Backfire and Hesitation
Wanted: Steering column and shaft for M38-1952, or late CJ2A
2024 CT. MILITARY VEHICLE SHOW AND FLEA MARKET- JUNE 15,2024
Brake Line
How to link full size photos in posts
Clutch release bearing support cast tab for return spring
T90 case replacement required?

Willys M Jeeps Forums


willysmjeeps.com :: View topic - M38 fording system vacuum leak?
 Forum FAQForum FAQ   SearchSearch   UsergroupsUsergroups   ProfileProfile   Log in to check your private messagesLog in to check your private messages   Log inLog in 

M38 fording system vacuum leak?
Goto page Previous  1, 2, 3, 4, 5
 
Post new topic   Reply to topic    willysmjeeps.com Forum Index -> Technical Knowledge Base
View previous topic :: View next topic  
Author Message
JeepdaddyRC
Member


Joined: Jan 10, 2020
Posts: 170

PostPosted: Thu Mar 02, 2023 9:21 am    Post subject: Reply with quote

RonD2, there are photos of my vacuum gauge connection to the intake manifold in my Feb 16 post. I followed the instructions on page 80 of TM 9-8012: "disconnect fuel and vacuum pump vacuum line at elbow located on exhaust manifold, and install vacuum gage adapter in elbow (fig. 22)."

My carb rebuild performed differently on different engines. I do not have Scoutpilot's vacuum of 23, but my vacuum of 19.5 is not bad.

I am out of ideas. I still suspect a vacuum leak. Since the carb likes choke, I have too much air or not enough fuel. Since I can't find an air leak, my next step is to send the fuel/vacuum pump to Scoutpilot. I have found him very helpful and a pleasure to work with.
Back to top
View user's profile Send private message
JeepdaddyRC
Member


Joined: Jan 10, 2020
Posts: 170

PostPosted: Sun Jun 04, 2023 8:29 pm    Post subject: Reply with quote

Update:
I now have a new head gasket, a rebuilt carb and a rebuilt fuel/vacuum pump (thank you ScoutPilot). New brass fittings and new vacuum lines. Confirmed fuel tank vent working. Timing 7-8 degrees. Have spark and air. New fuel filter. Fuel tank clean, fuel lines clean or replaced. New points and condenser. Gaps set to specs. Plugs look tan.

Still acts like a vacuum leak. Needs almost full throttle to start. Vacuum reading at 650-700 rpm is 18.5 But engine runs much better with 1/2 choke and vacuum increases to 19.5-20. Significant hesitation off idle and wants to die without 1/2 choke.

Can't locate a leak using propane enrichment and/or and carb cleaner. However, when I spray carb cleaner on the two fittings at the rear of the air cleaner, the rpms pick up and the engine smoothes out. This confuses me. I thought those air cleaner connections for the master cylinder and fuel tank were vent lines only and did not lead to vacuum leaks. The connections are tight.

This has been a challenge indeed, but perhaps this new info will help us solve the mystery. Thoughts welcome.


Last edited by JeepdaddyRC on Sun Jun 04, 2023 9:46 pm; edited 2 times in total
Back to top
View user's profile Send private message
wesk
Site Administrator
Site Administrator


Joined: Apr 04, 2005
Posts: 16225
Location: Wisconsin

PostPosted: Sun Jun 04, 2023 9:38 pm    Post subject: Reply with quote

Try to remember that air cleaner feeds your carb which is sucking on it. Anthing flammable you introduce up stream (AWAY FROM SUCTION) will increase the RPM as it finds it's way to the Suction source called your carb.
_________________
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
Back to top
View user's profile Send private message Send e-mail Visit poster's website
JeepdaddyRC
Member


Joined: Jan 10, 2020
Posts: 170

PostPosted: Mon Jun 05, 2023 10:53 am    Post subject: Reply with quote

Wes, you have a way of making things make perfect sense.
I could not have come this far without you and this great forum.
Would you agree the symptoms suggest a vacuum leak?
Back to top
View user's profile Send private message
wesk
Site Administrator
Site Administrator


Joined: Apr 04, 2005
Posts: 16225
Location: Wisconsin

PostPosted: Mon Jun 05, 2023 11:32 am    Post subject: Reply with quote

Maybe but still not sure. Could be vacuum or it could be mixture. Once you eliminate all vacuum leak options with a propane type check. The next check is mixture adjustment check along with a recheck of fuel pump pressure. Also if you have kitted the carb up make sure you have the right metering rod installed. A lot of kits come with both for the m38 & M38A1.






Here's a dual carb kit.

I wouldn't waste a lot of time worrying about a vac leak at the fuel pump. Has very little to no influence on manifold vacuum. The fuel/vac pump vac side only does one job. It increases vacuum suction to help the wipers perform adequately. If you insist on following a troubleshooting path towards the vac side of your fuel pump then you only need to perform one step. Remove the line from the intake to the vac side inlet of the pump and plug the hole in the intake.
_________________
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
Back to top
View user's profile Send private message Send e-mail Visit poster's website
JeepdaddyRC
Member


Joined: Jan 10, 2020
Posts: 170

PostPosted: Tue Jun 06, 2023 7:19 am    Post subject: Reply with quote

The carb has been apart many times, including a rebuild by Scoutpilot. The carb kit is from MWM. I confirmed accelerator pump and metering rod spring sizes are correct and in proper locations. The diaphragms are good and it is the correct M38 metering rod size. Scoutpilot drilled out the new low speed jet tube orifice to correct size with #70 drill bit and believed the orifice on the 3/16 carb vent line fitting on top of carb was too small. However carb to crossover vent is clear and no difference in performance with carb vent line on or off.

Regarding a vacuum leak at the fuel pump side, when I attach the vacuum gauge it essentially takes the pump and associated vacuum lines to wipers and distributor out of the equation. The vacuum gauge is plugged into the intake manifold port that normally leads down to the pump.

Carb base gasket and intake manifold to block mating surface would be my first suspect areas. Neither indicated air leakage to disrupt the mixture. Throttle shaft on carb would be my other suspect area, no sign of leakage there. Beginning to think the carb is haunted.

The only way this Jeep will start is to pull the hand throttle way out while cranking. This is different than my other experiences and seems inconsistent with a vacuum leak and more like a flooded engine. This one has me stumped indeed.
Back to top
View user's profile Send private message
JeepdaddyRC
Member


Joined: Jan 10, 2020
Posts: 170

PostPosted: Thu Jun 15, 2023 1:44 pm    Post subject: Reply with quote

Update: Mystery solved - it was a fuel delivery problem.

I installed a working carb (Carter WO). The M38 now starts easily, idles smoothly, has no hesitation on acceleration and the phut-phut from the tailpipe is gone. It is an unbelievable difference, it's like a new Jeep, sounds great and purrs like never before. ! asked my daughter to confirm I wasn't dreaming.

But now I need to return the borrowed WO carb. One option is to purchase a new repo Carter WO from Ron Fitzpatrick. If anyone has experience with those, I would appreciate a review.

But this M38 is mostly original and I prefer to keep it historically correct. Therefore if anyone has a working YS637S they would like to sell, please let me know.

Thank you to Wes, Rond2, and all that helped me with this mystery.
Back to top
View user's profile Send private message
RonD2
Member


Joined: Oct 02, 2014
Posts: 1887
Location: South Carolina, Dorchester County

PostPosted: Thu Jun 15, 2023 2:25 pm    Post subject: Reply with quote

Glad you found the problem!

I'm surprised to hear that a YS-637S that ScoutPilot rebuilt has a problem.
Before buying another (big bucks), have you contacted him to see if he'll fix it under warranty?
Just a thought.
_________________
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

Back to top
View user's profile Send private message Send e-mail
4x4M38
Member


Joined: May 30, 2014
Posts: 3440
Location: Texas Hill Country

PostPosted: Thu Jun 15, 2023 9:10 pm    Post subject: Reply with quote

Using the WO civvy carb eliminates a lot of stuff besides the YS637.

The carb may still not be your problem.

I’d send it to Scoutpilot and tell him about swapping to the WO, and ask him to stick it on his test stand.
_________________
Brian
1950 M38
MC11481
http://www.willysmjeeps.com/v2/modules.php?set_albumName=album372&op=modload&name=gallery&file=index&include=view_album.php
Back to top
View user's profile Send private message Send e-mail
JeepdaddyRC
Member


Joined: Jan 10, 2020
Posts: 170

PostPosted: Fri Jun 16, 2023 11:13 am    Post subject: Reply with quote

Brian, other than eliminating the tube to crossover pipe and using a mechanical accelerator pump and metering rod, what else does the WO eliminate? Why do you think the carb might not be the problem? All info is helpful from more experienced M38 owners. I do realize the YS vacuum operated systems are designed for fording, but since the WO was used on the CJ3A it is was a step in my trouble shooting. The starting, idling and performance improvements were unexpected and amazing. It sounded like a completely different engine with fuel delivered by the WO.
Back to top
View user's profile Send private message
Display posts from previous:   
Post new topic   Reply to topic    willysmjeeps.com Forum Index -> Technical Knowledge Base All times are GMT - 6 Hours
Goto page Previous  1, 2, 3, 4, 5
Page 5 of 5

 
Jump to:  
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

Powered by phpBB © 2001 phpBB Group
Forums ©

 



PHP-Nuke Copyright © 2005 by Francisco Burzi. This is free software, and you may redistribute it under the GPL. PHP-Nuke comes with absolutely no warranty, for details, see the license.