BREAKING UP

1950 - 1952, M38, questions, discussions, regarding anything related to the M38.
JMZ421
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BREAKING UP

Post by JMZ421 » Mon Oct 09, 2017 2:46 am

My M38 has been running really good all summer. A few weeks ago, she started to hesistate, misfire, around 10 Mph. Now, if you floor it in 1 st gear, there is no power and stumbles something terrible, around 10 to 15 MPH. She idles ok and starts right up. Per the manual, I cleaned plugs and even changed them with some old ones I had and no difference. I did change out the points and condenser as they were cheap. Cap and rotor look good. I think it may be the coil? I do have an extra but I thought would ask here. Thanks John


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Re: BREAKING UP

Post by dpcd67 » Mon Oct 09, 2017 7:03 am

It is usually fuel when that happens, but do your troubleshooting steps to isolate it. But I have had that happen and it was clogged fuel filter. Check float and bowl too. When the carb needs fuel, it is starved.
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Re: BREAKING UP

Post by Joe Gopan » Mon Oct 09, 2017 7:25 am

Your Carburetor may need a Kit, The Pump Diaphragm may have ruptured due to age and reaction of the rubber diaphragm to today's fuel. It's a common event in the YS M-Series Jeep Carburetors. They age and rupture, more so now with today's fuel.
All Jeeps with YS Carburetor can expect this.
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JMZ421
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Re: BREAKING UP

Post by JMZ421 » Mon Oct 09, 2017 10:23 am

Ok, this may explain why I cannot adjust the idle air mixture and why I get this unwanted rpm increase, if that makes sense. There are no vaccumm leaks as I checked and the fuel filter in the tank is newer. I will change that coil out just to see but my bet is on your answer. I will let you know and Thanks, John

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Re: BREAKING UP

Post by FrankenJeep » Mon Oct 09, 2017 1:33 pm

And avoid Ethynol gas. It will create moisture in the tank and wreak havoc with the running. Try also, draining the tank and put in a fresh tank of non-ethynol gas. Might save you some $$$$.
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Re: BREAKING UP

Post by Joe Gopan » Mon Oct 09, 2017 1:46 pm

If you have never worked on the YS before, be careful not to tip the float chamber upside down, that little rectangular brass weight that just fell out had a check ball under it.
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JMZ421
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Re: BREAKING UP

Post by JMZ421 » Mon Oct 09, 2017 3:01 pm

Got hime from work and replaced the coil with spare I had and that was not the problem. I pulled the carb just now and I am sending back to the vendor I purchased from just over a year. He is very nice enough to look it over for me to see what's up as it is close to the warranty period. I will make a note of that ehthynol issue. I will get back to you. Thanks again for your help. John

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Re: BREAKING UP

Post by JMZ421 » Wed Oct 11, 2017 1:51 am

Hello. Will 91 octane ethanol free fuel be ok in the m38? I found one station by me that sells this. Thanks. John

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Re: BREAKING UP

Post by Joe Gopan » Wed Oct 11, 2017 4:45 am

Won't hurt a thing.
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JMZ421
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Re: BREAKING UP

Post by JMZ421 » Sat Oct 21, 2017 2:25 pm

Today I installed the rebuilt carb for my M38 and it still has no power. She idles Ok but if you throttle up quarter of the way starts to break up and again no power. I changed everything in the distributor and the radio condenser also(that second condenser). I attached a hose to the fuel pump and it fills up rather quickly. I pulled the muffler and ran up the street, no difference. The manual states to run a compression test. I guess I will do that next to make sure that is ok. But, she ran fine all summer and does not use a drop of oil. The plugs looked OK when I pulled them out, even swapped in some spares, no difference. Coil aslo. I checked the timing and the I assume the advance springs are OK if you throttle up and the timinig marks move. Question: could a fuel pump be defective at higher rpms'? not pumping enough fuel. I have nothing in the tailpipe like fuel or anything.

Any ideas, besides the compression test to check the internals. Thanks John

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Re: BREAKING UP

Post by Joe Gopan » Sat Oct 21, 2017 3:54 pm

Spark Plug wires, perhaps, these wires do fail at times Remember not to wrench them tight onto the spark plugs as it can roll over the threaded end of the spark plug creating a wire edge that will grip the orange insulation and cause it to pull apart. Mechanics learned to tighten these wires finger tight at the plugs as the Jeep was not going fording.
The owner made a video of the fault.
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LIFE MEMBER AM LEGION-40/8-DAV
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Re: BREAKING UP

Post by JMZ421 » Sun Oct 22, 2017 4:18 am

Luckily I saved the old wires and will put them back on. The current wires were placed on a couple years ago. I remember you telling all of us not to tighten them too much, which I do not. I will replace them today and get back. Thank you, John

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Re: BREAKING UP

Post by JMZ421 » Sun Oct 22, 2017 5:52 am

Ran out just now and swapped those wires, no difference. I can drive 5 mph and it is fine, step on the gas stumbles and bumbles and does not power up at all. Starts, Idles just fine and engine is quite. I am wondering if the fuel pump is the culprit under load. Would a bad coil cause this?
Both my coil are very old, maybe coincidence that they are just both bad. John

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Re: BREAKING UP

Post by Joe Gopan » Sun Oct 22, 2017 6:20 am

When you inspected the carburetor did you note if the Metering Rod Diaphragm had the spring with the finer wire? There is a light and heavy spring, heavy spring is the pump spring.
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HONOR GRAD-WHEELED VEHICLE MECHANIC SCHOOL 1960 - US ARMY ORDNANCE SCHOOL(MACHINIST) ABERDEEN PG 1962 - O-1 BIRD DOG CREWCHIEF - 300,000+TROUBLE FREE M-38A1 MILES
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Re: BREAKING UP

Post by artificer » Sun Oct 22, 2017 7:19 am

Point gap closed up will cause this lack of acceleration power type issue.
This because the coil does not have time to saturate properly.
Points fitted dry with no lube on the rubbing block or cam will close up rapidly.
EZ to check & eliminate immediately by using a dwell meter. Nothing needs removing or disconnecting to do this check.

Think about what has been done changing parts incl. carb coil etc. None altered anything so it is something that hasen't been eliminated.
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