What's my problem?

dod03-52 · Post by **dod03-52** » Wed Sep 15, 2010 9:39 am

First start of the morning----no choke--starts hard, runs rough, blue smoke for about 20 seconds
30 seconds later---runs great
After shut down:
5 minutes---starts right up
30 minutes--cranks--runs rough for 10 seconds
1 hour--cranks 10-20 seconds--runs on 1-2-3 cylinders---lots of blue smoke until it blows it out
Carb leak into the manifold?

Post by **wesk** » Wed Sep 15, 2010 11:33 am

What model jeep? If M38A1 early or late vent system?

Blue smoke is oil. Sources are PCV system, fuel pump internal oil leak,
or on the F134 leaking intake valve stems/seals.

dod03-52 · Post by **dod03-52** » Wed Sep 15, 2010 3:51 pm

Duh! It is a 53M38, all orginal---I should not say the smoke is blue but it sure smells like raw fuel...It starts like the choke is pulled out every time.
How can I check for a static fuel leak from the carb to the manifold?

dod03-52 · Post by **dod03-52** » Wed Sep 15, 2010 3:52 pm

Duh-Duh! it is a 52 M38----got a bad cold--need more Nyquil!!

Post by **wesk** » Thu Sep 16, 2010 10:34 am

Fuel rich exhaust is black. If you are actually that rich I would look closely at the two rubber diaphragms for the accelerator pump and metering rod. If these have deteriorated due to the ethanol in modern gas you will have to replace them before pressing on.

Items Y and DD in the above parts illustration.

dod03-52 · Post by **dod03-52** » Thu Sep 16, 2010 7:29 pm

I tried something today. I ran the engine for 5 minutes, took the carb loose enough to get a thin strip of v-shaped metal under the carb base and watched. In 30 minutes I had a conciderable amount of fuel in a Nyquil cup. I could include pictures if I knew how to attach them. This carb is less than 6 months out of overhaul.

Post by **wesk** » Thu Sep 16, 2010 9:50 pm

You said in just a few moments the engine would smooth out and run fine. Therefore the 5 minute later incident is not really germain to your starting problem.

The fuel leak in your plastic cup could simply be a boiling of the fuel in the bowl. Using the thin instead of the correct very thick carb to intake gasket can transfer way too much heat to the carb. Also a stuck heat riser can cause the same.

You say a less than a year rebuild. Was an old NOS kit used in the rebuild or a modern kit with modern rubber diaphragms?

This is the correct thick base gasket for the M38 carb. The metal "V" improves atomization of the fuel at low RPM in cool weather.

dod03-52 · Post by **dod03-52** » Fri Sep 17, 2010 5:46 am

First, I appreciate all the help and experience that I am getting from you all.
1. I have the thick gasket but without the v-installed--the heat riser works great and the engine manifold was only "warm" when I did the test.
2. The carb was rebuilt by who ever does them for MWM.
3. I had a 46 CJ2A and a 51 CJ3A and they never started this way.
Is this a YS problem ? It is embarrassing to be at a store and the restored jeep belches out smoke when it starts.

Post by **wesk** » Fri Sep 17, 2010 10:23 pm

One thing unique to the YS series are the vacuum operated metering rod and accelerator pump.

Look hard at the assembly illustration for the position of the diaphragms vs the springs. Then open up the two diaphragm covers and confirm the correct placement of the springs. Also confirm the correct spring is on the correct side.

In the original version of that drawing which is from the Carb TM the positions of BB and DD were reversed. Anyone following the TM could easily reverse them causing your symptoms.

In addition the MWM carb kits contain both the M38 (YS637S) and M38A1 (YS950S) metering rods so make sure you have the correct 75-595S rod in your carb.

dod03-52 · Post by **dod03-52** » Sat Sep 18, 2010 4:21 am

Thanks Wes,
The next morning---the carb had dripped more fuel into the cup--
I removed the drip catcher, bolted the carb down and fired her up.
It cranked for a few seconds to refill the bowl and ran beautifully!!
No roughness, no smoke--sounds like a sewing machine.
I sent the pictures to John at Mid West Military and he will return the carb to his rebuilder.
Will be putting the jeep to bed for the winter in a few weeks---this is Minnesota and it is mid September.

Post by **wesk** » Sat Sep 18, 2010 1:04 pm

You guys bed them down early!! I am a hundred miles east of you and we will be doing convoys until the last week of October.

Only takes five minutes to open those diaphragm covers and check.

dod03-52 · Post by **dod03-52** » Mon Sep 20, 2010 6:34 am

Wes,
Before I pull the Metering rod out, how can I tell if the correct rod is installed when I remove it?
Thanks,
Bob in MN

Post by **wesk** » Mon Sep 20, 2010 8:57 am

The part number is on the genuine parts 75-595S.

If they are aftermarket rods check the measurements.

The main thing is placement of the springs thick vs thin and relative position to diaphragm.

dod03-52 · Post by **dod03-52** » Mon Sep 20, 2010 7:26 pm

Wes was right---again!
The longer spring was on the metering rod, but on the rod shaft--not under the cap like it is supposed to be. The engine idles and runs better but I still have the fuel leaking into the intake manifold after shut down. It still starts hard and rough after sitting for a hour or longer. I will contact John at MWM. It runs much better but what else is wrong with the carb?