Do I need a carb rebuild?

[sergeantfirkus]

Before I go down the wrong path yet again, I thought I'd ask the masters!

I bought this M38 jeep in October and it ran decent. Now it wants to have a little choke to run smooth when I depress the peddle to accelerate. It runs fine at a steady speed but when I speed up it sputters. If you pull the choke out 3/8 of an inch it runs great.

I replaced the CJ tank with a MD Juan replacement tank. New fuel pickup assembly from Midwest Military with the after-market filter in it. I also remade the steel lines from the pump to the carb and the fuel pickup over the top of the tank.

Additionally, I made a new vacuum line for the distributer and hooked it up to the "TEE" that comes from the vacuum pump side of the fuel pump and to the wipers. I didn't put a restriction (.040 I believe) in this line though I read about it on the CJ3 site. This distributer line was hooked directly to the intake manifold before. Could this be part of the problem?

The jeep looks to have been worked on shortly before I bought it (possibly to make it run to sell) as the coil and screws holding it in the distributer look shiny new. The top of the carb has some new screws in it also.

What I've checked:
Adjusted Idle mixture to best idle approx. 1 1/2 turns out.
Fuel pressure checked: 5 psi
Distributer points checked and gapped to .020 inch.

Haven't checked the timing.

My next step is to clean the carb, hoping to find some foreign matter that might have got into the system when I removed and remade the lines.

Any suggestions?
If I do need a kit, who sells the good ones? Kits with instructions are always helpful.

Thanks,
Greg V.
_________________
1951 M38

[wesk]

Hello Greg,
I have been a professional mechanic since about 1966 and was a race car builder and runner for several years before that.

One important lesson I have learned over those years is to troubleshoot in an orderly manner. This means check and record ALL the engine's operating parameters before fooling with anything. Next, if the manufacturer's manual has a troubleshooting guide I use it step by step.

What you describe suggests several problems. Generally when one must use the choke to improve the fuel air mixture thus smoothing out engine operation they are decreasing air flow thus they are changing the air/fuel ratio by lowering the percentage of air. This means you either do not have enough fuel supply or there is too much air.

Since you have made changes in several areas that include vacuum connections, fuel tank and supply I would carefully check each.

A fuel tank that has no vent will restrict fuel flow. Check this by removing the fuel cap and running the engine.

A small air leak in a fuel line connection before the pump will allow the pump to suck air and never show any fuel leakage. This will reduce fuel flow. To check this plug fuel tank vent and seal cap then take fuel line from tank off the pump and apply 1.5 to 2.0 PSI to it and using a spray bottle of soapy water check each connection for leaks (bubbles) after spraying the soapy water on the connection.

Excess air can be from a gasket leak, a PCV valve stuck open, an intake manifold leak from a crack or loose hardware. Check this by using the propane enrichment test.

Finally you mention a vacuum advance on the distributor. The M38's original distributor only has a centrifugal advance. If you have the original military distributor there are two metal lines to it. One connects to the crossover duct to allow fresh air into the housing and the other connects to the vacuum/wiper "T" for suction to pull clean, cool air through the distributor housing to eliminate the buildup of gases and help coll the coil. This line must have the .040 restrictor in it.

I would have checked timing the day I brought the jeep home because you can only trust one person on this planet! If you find the water proof shielded ignition a pain to work with for the timing check and you don't have the test adapter kit for all the water proof electrical system testing then just check the timing the old fashion way with a piece of paper or a test lamp. If your distributor is original M38 than you should have an initial static setting of 5 deg's BTDC at 650 RPM. At about 2000 RPM you should have attained another 10 to 11 degrees of advance from the centrifugal weights for a total advance of 15.

The test lead adapter sets run from $40 to $75. The best place for a quality new materials overhaul kit is Midwest Military. Be very carefull to follow the correct blowup drawing and keep all parts in the correct position. The springs at the metering rod diaphram and the accelerator pump diaphram are different. Also some of the the parts blow up drawings are not correct in the placement of one of the springs. The Carter carb overhaul manual pages applicable to the YS637S carb are uploaded on our downloads page.
_________________
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

[sergeantfirkus]

Wes:

I've never made a living as a mechanic. But on the farm it's 40% mechanic, 50% janitor, 10% actual farm work!

This jeep has an MB engine under the the MC accessories. Not exactly sure about the timing procedure.

It does have the 24v military distributer. Both lines are hooked up. I will make a .040 restriction for this line. I referred to this line as a vacuum line since it went to the vacuum side. There wasn't any restrictor before.

I understand the idea of the fuel lines sucking air. (possible since they were touched)
The fuel pump pressure read 5psi then held 2.5 psi after I stopped cranking.
After disconnecting the gage I cranked and watched the fuel flow into a can the flow seemed fine chugging fuel out at each pump stroke.
When a pump sucks air generally it loses prime or mixes air into the liquid correct?

The vent line to the fuel tank is new. The cap is new and has the valve in it which I confirmed in the open position. The PCV valve was removed and cleaned too and seemed to function and re-installed it the correct direction.

Concerning vacuum leaks after checking by propane enrichment, what should I be looking for in a vacuum reading?

I'll work thru your suggestions and report back.

Thanks for you help!
Greg V.
_________________
1951 M38

[wesk]

Sorry about the way I opened my post. It was not my intention to compare our qualifications. Since it was my first post to you I felt I should introduce myself and my experience so you would know from where I speak.
I'm not quite a farmer but my wife's love of horses has me doing a lot of agricultural type work. I have a 47 Allis B I use for moving manure and snow and I have a rusty tank so every now and again I am doing what I have to do this morning. Removing and cleaning the carb. I have been searching for a better tank and I am also looking for one of the two-point hydraulic rams.

Anyway, back to jeeps. What to expect on a vacuum system test gage is covered in detail in the TM 9-8012 Service manual for the M38 on pages 77 thru 80.
_________________
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

[sergeantfirkus]

Wes:
Absolutely no offense taken here regarding qualifications. Sometimes words don't come across as well as conversation. I just wanted to let you know I have some experience fiddling in the mechanical world. Sometimes it helps to let others know this so they can guide their answers along a different level of explanation.

I'll check out the manual regarding vacuum and other items and report my findings.

I really appreciate the time you take to answer on this forum.

Thanks,
Greg
_________________
1951 M38

[sergeantfirkus]

Today I put the .040 restriction in the distributer line.

Removed top of carb and checked for cleanliness, made sure the needle valve & seat and float were in good order.

Verified that the choke butterfly was all the way open when the cable was pushed in.

Hooked up a vacuum gauge to the manifold and it read 18" Not ideal. Connected to the wiper TEE (thru the fuel/vacuum pump) it read 17". So I'm losing some vacuum there. The gauge fluctuates about 1/2" + or - either location.

Closed the fording valves which made no difference in the vacuum reading.

Applied propane thru an unlit blow torch and the results were inconclusive. I could only detect an increase in RPM if I took the vacuum gauge off and let it suck propane in. There must be a technique that I need to learn.

The engine runs the same. Needs slight choke to accelerate. Pulls fine in first gear, second and third want slight choke. No choke needed to maintain speed.

Loosened the distributer to attempt a check on timing. Broke the bolt off underneath. Spent the rest of the afternoon removing, extracting, replacing. Will check the timing next time.

Greg
_________________
1951 M38

[OKCM38CDN]

This may not be ther proper method...

I use a can of carb cleaner to check for vascumme leaks... Engine at idle and spray the manifolds and base of the carb... same emthod as propane just a different accelorant...

Make sure your inverted flare connections on the vacume lines are inverted flare and not straight flares... also mke sure all connections are tight (you probably have done this already)...

I had to take my manifolds (both) to a machine shope and have them mated then machined to get a good mating surface for stopp a vacume leake at the block...

Hope this helps...

[sergeantfirkus]

Hal:
How bad was your vacuum leak? Did you take a reading.
I did make inverted flares.
Will try to do a leak check with carb cleaner or something.
The jeep ran good before all the changes, so it most likely is something I goofed up!

Greg
_________________
1951 M38

[OKCM38CDN]

My leak was bad, had to run choke like you do... Had trouble starting it up and keeping it running... I went thru everything and found manifold leaks that is why I went with the machine shop... best hundred dollars I put into the motor...

Hope you find it...

[sergeantfirkus]

[wesk]

Go to downloads at top of this page. Click M38 "Drive Train" then click "Engine" then click on "YS Carb Manual" and you'll get the 21 page PDF doc.
http://www.willysmjeeps.com/downloads/YScarb.pdf
_________________
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

[sergeantfirkus]

I was only a couple of clicks away! Didn't think to look under "drive train"
I'll look it over.
Thanks,
Greg
_________________
1951 M38

[sergeantfirkus]

Pulled the top of the carb. Float was set way high, reset to 1/4" per Carter info. No change in the way that it runs.

Not sure of the timing. This M38 is sporting an MB block, but has MC accessories. There are marks on the cover behind the crank pulley. The pulley doesn't have a timing hole in it, but has a notch in it. If I attempt align the notch with the first mark, it's way too far retarded. So, I put the distributer back where I marked it before moving it.

Took the meter rod diaphragm off the front of the carb. It's like new. This carb has been worked on prior to my ownership.

Next?

Thanks,
Greg
_________________
1951 M38

[wesk]

It is possible then that your carb has been buggered or played with but not overhauled. It is still possible you have some garbage trapped in a passageway or holding something part open. How does the accelerator pump diaphram look. Any pin holes or cracks in it will allow extra fuel to get sucked into the carb.


Sooner or later you will have to step up to the timing plate and swing. Now is the time. Do you have the small inspection window above the starter for the flywheel timing mark?
_________________
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

[sergeantfirkus]

Wes:

I agree the carb could be buggered. Though everything I look at on it appears to have been renewed. I'll tear it down and see what the check balls and pump diaphragm look like.

I'm swinging at the timing. I grabbed a wire off an avaition harness and made a wire to attach the inductive pickup of my timing light to. Now I just need to know where to point it!

The timing by the flywheel is referred to in the TM 9-8012 but I didn't find a picture or a location in the ignition section.

Can you see the window from the engine side above the starter?
Do you use a timing light at that location?
Is 5º BTDC correct for the MB too?

Greg

PS: Regarding the Allis B, are there any gas tanks for them being reproduced? You are looking for the cylinder that goes on the two point hitch? I bought some parts from (Junky) Ray Erickson up near Gays Mills or Soldiers Grove WI. I have a MM RTU that I painted up and that's MM territory up there. He's got lots of stuff, all the brands.
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1951 M38