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UPDATE: IDLE PROBLEM SOLVED - pinhole found in High Speed vacuum operated metering circuit diaphram. This gave a positive feedback path for gas to loop from the float chamber to the vacuum vent of the carb. New diaphram and now the idle is nice and smooth.

SPARK TROUBLESHOOTING THIS WEEKEND! Thanks for all the input too.


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A couple of weeks ago I fired up my M38 to find no oil pressure. I changed out the "NOS Oil pump" that I got from a vendor for a mellings pump from my engine kit.
Now It fires up and reads 40-45 psi on two separate mechanical gauges.
A couple of things:

Idle is very rough and it seems to be flooding and smoking. I reset the float level per the Carter manual and it still seems to flood. Looking down the throat there seems to be a puddle of fuel in the intake manifold.
More reading is required to troubleshoot this one.

There is a spark when I connect the batteries. Measuring about 30ma of current, something is pulling current when all systems are shut down. This can be troubleshot through isolating circuits.

Dwell/timing was set to correct but given some of the other reports of caps and condensors failing, these will be easy enough to substitute. The engine revs fine. it just wont idle. Also, there may be a vacuum leak that I am overlooking.

There was a knock - it turned out to be a bent crank pully. replaced and problem solved.

There was a nasty squeal > tightened fan belts. solved.

There was a water leak behind the starter - a crack? No..turns out the water temp sender is weeping and the drops landed just behind the starter. That one gave me a heart attack.

Polarizing the gen before connecting batteries assured the charging system was in shape. It reads CHG.
Fuel gauge is working.
Temp gauge needs a new sender but the gauge works per the troubleshooting docs when substituting a proper resistor.
Oil pressure gauge reads low. There are two problems. The sender shows the wrong resistance at pressure and the gauge is also out of calibration per the resistance tables that I have read. at idle it runs about 9 ohms which shows about 30psi. For now the mechanical gauges will stay connected in paralell and a test jig can be set up for other senders.

The clutch, trans and transfer all seem to be doing their job on a short roll out the driveway and back in.

Overall with some troubleshooting we may have another M38 on the road this spring. Fingers are crossed.

Tom

Hello Tom,
Was there no snow in your driveway? Looks like you have a handle on most of your issues. The gas puddle looks like a stuck float, high fuel pump pressure or a crack in the carb bowl interior surface.

Tom,

Do you have the dash primer pump installed? Pumping too much can cause a puddle fo fuel.

The electrical system will spark a little at the battery terminal when connecting the batteries. I don't know the exact ohm reading for that. They all sound like small problems that can be fixed easily.

With the foot of fresh, heavy, rock hard snow/ice in the driveway it will be a while before backing out to fool with the engine again.

I did not install a hand primer.

A fuel pressure guage can be put in line easily enough so that's a step to take and also the parts bin just gave up a NOS carb float needle and seat from a "Carter 1710 YS Willys MD Jeep Army M38A1 underwater" kit. I'm guessing it will fit the M38. I rebuilt the carb a few years ago and used a new needle and seat then but thats the first obvious problem to change out.
In 1953 a YS was $19 with a $5 core charge. Will have to scan the March '53 spec sheet for posting.

FYI on initial startup a mightyvac pump was used to suck fuel through the fuel pump and give it a prime. That saved a lot of cranking.

TM

Electric spark at the battery terminal may be the
capacitor charging up. Folks on this forum said it
was normal.

Jim in Darkest Arkansas

With all switches off there should be no current flow therefore NO spark when removing either battery cable. I am sure Tom knows this which is why he mentioned troubleshooting by eliminating one circuit at a time. The normal culprit of this current drain is the start switch on top of the starter.

The normal culprit of this sparking is the starter switch on top of the starter. They get a carbon build up inside after years of use and it allows the current to flow just enough to get this spark.
Worth a look.
John

At least John agrees with me!

Almost word for word,like he's trying to copy you.

Not always Wes, but most of the time. Sorry for the look of plagiarism!
John

PS Magazine states that when connecting the battery terminals a small spark when connecting the last terminal is normal. PS magazine said it had to do with the capaciter in the voltage regulator.

I don't know how much voltage you have going on so I don't know if yours is normal Tom.

That's a very, very small weak spark you can barely see. That's easy to isolate by removing the firewall harnes to regulator plug.

Hey Wes,

Some of us younger guys can see them more easily than our elders can if you look for it when you hook the battery up.

Again when troubleshooting you are suppose to be checking for a spark when you disconnect not when you hook up. The condenser charge thing is a momentary thing and to continue your troubleshooting of current loss ignore that momentary spark and press on with a test lamp connected between the ground cable and the engative cable. As long as the light glows you have a current draw that is not normal.

Thank you Ryan Millier for posting the PS article
on a spark when connecting to the battery on an M38
et al. I knew I'd seen it somewhere on the Forum.

It IS a LOT smaller than the spark you get with the
OFF-ON switch in the ON position (not recommended.)

Jim in Darkest Arkansas, 66 year old eyes.