Carbs...

jsnwalker · Post by **jsnwalker** » Sat Feb 04, 2017 1:01 pm

First off, I apologize for this question... I'm sure this question is right up there with something like 'which pedal is the accelerator' but being that this is my first experience with a carb, I gotta ask it.

I bought my M38 from a guy in Iowa were elevation is roughly 500'. I live up in the mountains were elevation is 5000' give or take. Using my non-existent carb knowledge, I believe that they need to be 'adjusted' to the elevation you are at otherwise it won't run well. Also, even in Iowa, the jep was running rich, which I believe is related to the carb, so I'm even more so worried about being up higher.

Is my thinking at least somewhat valid or I am I worried over nothing? I need to fix it running rich regardless (no idea on how to do that yet...) but the elevation piece is unknown.

Any input/advice/ridicule would be much appreciated!

-J

4x4M38 · Post by **4x4M38** » Sat Feb 04, 2017 1:55 pm

J,
It could be something as simple as a dirty air cleaner.

To be able to help it's important the folks here know how much if any original equipment is on your M38.

For instance, depending on the level of maintenance or civilian modifications a 67 year old M38 could have at least one of three carburetors installed, the original YS637, a Carter W-O, or even a Solex.
All three have different adjustment and troubleshooting procedures.

That and other things such as the vehicle still having all, a portion, or none of the original fording and ventilating system, and/or vacuum wipers, and original AC fuel/vacuum pump, could be relevant to your issues.

Hope this makes sense.

Photos help a ton as well.

BTW, there are at least two board members in the Salt Lake City area.

Take care,

Post by **wesk** » Sat Feb 04, 2017 2:38 pm

Hello Jason,
Welcome to our web site. Since your post was a technical question not the begining of a project trilogy i moved it to the technical board.

It is always best to first describe your equipment or state the M38 is bone stock.

I'll reserve offering any advice to later when you tell us what you have.

Things such as: which model engine, which model carb, which model fuel pump, with/without fording system plumbing and etc.

Below are photos of a new in the crate M38 factory engine stock with stock fording system plumbing and stock PCV system.

jsnwalker · Post by **jsnwalker** » Sat Feb 04, 2017 5:08 pm

Hey guys, thanks for the tips. I will post more information/pics of my M38 once I can. It won't actually make its way to SLC for another 2-3 weeks, I was just hoping to get a jump start on it.

Once she is safely in my driveway, the fun will begin!

-J

Boze · Post by **Boze** » Tue Feb 07, 2017 9:16 pm

Dude,

You're in luck. There are guys that are experts in the fine tuning and repair of the M38 that roam this site regularly. So don't be worried about dumb questions because we have all been there!

A bit of advice, look through the download section of this site and get your manuals if you don't have them already. They will prove to be priceless.

After that, my motto is details, details, details. Meaning, there is always one more thing to check.

Welcome to the hobby.

jsnwalker · Post by **jsnwalker** » Tue May 16, 2017 9:48 am

Alright, long time coming but I'm ready to start work on the carb and motor. After digging in a bit more, I'm pretty sure that I have a Carter W-O carburetor and that the majority of the motor is stock. The PO put a K&N air filter which I will get cleaned up to make sure that isn't holding performance back and I just installed a new high torque starter since the one I pulled off was useless.

I can get the jeep to start and idle right away, generally turns once or twice before firing up, and I don't really need to use the choke but I cannot climb a hill with a 4-5% grade that I live on even in 4WD low. The whole jeep just bogs down and dies.

There still are some issues with the jeep I need to fix; rear main seal, new oil pan, multiple exhaust leaks to name the big ones, but everything else seems to be running great. I am a little low on gas which could be causing some of my problem, but I have an electronic fuel pump that should be able to supply enough gas with how much is in the tank. Just did a compression test with a cold motor and got 90psi in each cylinder. Figured once it warms up and things seal up better, I can hit 110psi.

Anyway, I have always been told that any vehicle with a carburetor wont' run well when you go from from 500' to 5000' without some adjustments/rejetting the carb. Do you guys agree?

Post by **wesk** » Tue May 16, 2017 10:06 am

Again offering advice with little data to make a determination from is tough.

Compressions are a relatively accurate indicator of cylinder to valve to piston seal condition but a leak down pressure test is a much more accurate troubleshooting tool.

Your first move should have been cold compressions checks and timing checks.

You next move should have been hot compression checks, hot vacuum readings and fuel pressure/flow raedings and then while the engine is still warm another timing check. (Note: Timing check means both static and dynamic including governor operation)

The next move is to post the recorded findings of each test here and then the members will have some data to form opinions with.

Anyway, I have always been told that any vehicle with a carburetor wont' run well when you go from from 500' to 5000' without some adjustments/rejetting the carb. Do you guys agree?

That depends on the carb and it's current settings. You would have to confirm current jetting size and doublecheck float setting. Electric boost pumps are a lazy man's solution to symptoms that require much more attention. You did not mention if the output pressure of your electric pump is regulated in any way?

jsnwalker · Post by **jsnwalker** » Tue May 16, 2017 10:28 am

Alright, sounds like I'm jumping the gun a little bit again. I didn't want to get the motor warmed since I have oil dripping everywhere right now and no gauges except the oil pressure gauge to check readings. I have all the gauges and gaskets/seals I need arriving Friday to fix everything, then I'll do as you outlined Wes. Gives me time to learn how to do a leak down test and timing check the correct way as well.

Post by **wesk** » Tue May 16, 2017 11:17 am

A picture is worth a thousand words, literally in this hobby. Post a few photos of your engine. Useful photos that show adequate detail. Post the casting number of your engine: (Lower right edge of block). Post your engine's serial number: (Above the water pump). Never know, you may have an industrial L134 engine with the tiny intake manifold.

jsnwalker · Post by **jsnwalker** » Tue May 16, 2017 9:28 pm

Alright, here are some photos of the motor and up close on the carb.

Hopefully those help out more than my poor attempt at describing something I know nothing about!

RICKG · Post by **RICKG** » Wed May 17, 2017 8:27 am

A few observations:
1. RMC (replacement) motor.
2. 12V alternator conversion w/gear reduction starter.
3. WO carb w/electric fuel pump.
4. Heat riser spring and weight missing, the flapper may be stuck.
5. PCV system missing.

jsnwalker · Post by **jsnwalker** » Thu May 18, 2017 3:55 pm

1 - I did see it was a replacement motor but everything I can see leads me to believe it is an exact replacement.
2 - 12V conversion was done by a PO but the starter I ordered and installed. Old starter was completely useless.
3 - So I do have a Carter carburetor it seems. All I see with the fuel pump is a line from the tank to an inline filter with a line to the pump itself and then a line to the motor. I don't see anyway to regulate the pressure of the fuel line.
4 - Good eye. Will order those parts and install shortly. I only plan on driving this during the summer so no cold starts.
5 - Again, good eye. Haven't done much research on the motor yet so I didn't notice that. Will get those parts ordered as well.

Post by **wesk** » Thu May 18, 2017 6:13 pm

You missed Rick G's point.

The heat riser does make winter starts and warmups easier.

However a heat riser flapper valve with no way to control it can adversely effect the operation of your engine all year long. You do need to fix the heat riser at the earliest opportunity!

I would suggest fixing the PCV system at the earliest opportunity as well.

I am not sure of your meaning when you say:

everything I can see leads me to believe it is an exact replacement

The only thing I see is a 1952 or newer casting with an RMC serial. The rest of the bare engine assembly could be 80% after market for all we know. None of the accessories mounted on the engine belong on an MC or RMC engine.

The Carter WO has two clues on the carb itself. One is the word "Carter" and the other is the abbreviation "WO". The only thing missing is the WO model number tag.