M38a1 carburetor problem

1952 - 1968, M38A1, M170, questions, discussions, regarding anything related to the M38a1 series.
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Dude24578
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M38a1 carburetor problem

Post by Dude24578 » Thu Jan 10, 2019 6:14 pm

I have a 63 m38a1. I started to run rich, running rough with black smoke from the exhaust pipe. I adjusted the the fuel air mixture and it improved.
The problem returned. One day it shut off and wouldn’t restart. I decided to give it a tune up since it had not been done in a long time. I have replaced the spark plugs, spark plug cables, points and condenser, distributor cap and rotor and coil. It still would not start.
I decided to replace the carburetor. I order a carburetor from Midwest. It started immediately but was running rough. I adjusted the mixture and it seemed to be running fine. Took it for a drive and it started to run rough and eventually shut off and would not start.
Now it will start but is running extremely rough like it is only firing on one or two cylinders. I disconnected the vent line on the top of the carburetor and started the engine. When it stopped running, probably an oz of fuel spurted from the vent line.
Now I’m thinking vacuum issue??

Thanks in advance for your help.

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Scoutpilot
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Re: M38a1 carburetor problem

Post by Scoutpilot » Fri Jan 11, 2019 4:30 am

1. Is this a correct F-134 for the M38A1?
2. Is this a correct YS-950S carburetor?
3. Is the Fording System installed?
4. If so, are all of the valves open?
5. Have you driven this vehicle with the valves closed for more than 15 minutes?
6. What is the current setting for your Idle Mixture Screw?
7. What is the idle RPM?
8. Fuel tank clean?
9. Fresh gasoline? How old is it?
10. Air cleaner clean?
11. PCV system functioning?
'70-'71 'A' Batt., 377th FA, 101AB
(Slicks and LOH's)(Col's LOH Pilot)
'71-72 CHARLIE TROOP,
16TH AIR CAV, 1ST AVN BDE (AEROSCOUTS)
LOW LEVEL HELL.
'46 CJ2A
'47 CJ2A
'48 CJ2A
'48 B1PW126
'69 CJ5

Dude24578
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Re: M38a1 carburetor problem

Post by Dude24578 » Fri Jan 11, 2019 8:08 am

1 yes
2 yes
3 yes
4 yes
5 no
6 1 1/2 turns
7 does not run enough to measure rpm
8 fuel tank is clean
9 fresh 90 octane ethanol free
10 air cleaner appears clean
11 I am unfamiliar with pcv system. Please explain.

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Scoutpilot
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Re: M38a1 carburetor problem

Post by Scoutpilot » Fri Jan 11, 2019 8:14 am

Is the carburetor a rebuilt unit?
'70-'71 'A' Batt., 377th FA, 101AB
(Slicks and LOH's)(Col's LOH Pilot)
'71-72 CHARLIE TROOP,
16TH AIR CAV, 1ST AVN BDE (AEROSCOUTS)
LOW LEVEL HELL.
'46 CJ2A
'47 CJ2A
'48 CJ2A
'48 B1PW126
'69 CJ5

Dude24578
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Re: M38a1 carburetor problem

Post by Dude24578 » Fri Jan 11, 2019 8:35 am

It is


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Scoutpilot
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Re: M38a1 carburetor problem

Post by Scoutpilot » Fri Jan 11, 2019 8:46 am

It is possible that the PCV system has become clogged. Look at the driver's side of the motor for what is shown in the photo. Just above the fuel/vac pump is the plumbing for the PCV (Positive Crankcase Ventilation) system. Remove it. Clean it thoroughly. Reinstall it. The PCV valve itself should be capable of disassembly for cleaning. CAUTION: it only functions when reassembled correctly.


Unknown-2.jpeg
Unknown-2.jpeg (8.76 KiB) Viewed 57 times
PCV-1.jpeg
PCV-1.jpeg (8.15 KiB) Viewed 57 times
Last edited by Scoutpilot on Fri Jan 11, 2019 8:52 am, edited 1 time in total.
'70-'71 'A' Batt., 377th FA, 101AB
(Slicks and LOH's)(Col's LOH Pilot)
'71-72 CHARLIE TROOP,
16TH AIR CAV, 1ST AVN BDE (AEROSCOUTS)
LOW LEVEL HELL.
'46 CJ2A
'47 CJ2A
'48 CJ2A
'48 B1PW126
'69 CJ5

Dude24578
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Posts: 5
Joined: Thu Jan 10, 2019 4:36 pm

Re: M38a1 carburetor problem

Post by Dude24578 » Fri Jan 11, 2019 8:47 am

Side note: I have driven this Jeep over the past couple of years on ethanol gas. Could this have damaged something in the fuel system?

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Scoutpilot
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Re: M38a1 carburetor problem

Post by Scoutpilot » Fri Jan 11, 2019 8:53 am

Ethanol is typically very harsh on the diaphragms in the Metering Rod and Accelerator Pump.
'70-'71 'A' Batt., 377th FA, 101AB
(Slicks and LOH's)(Col's LOH Pilot)
'71-72 CHARLIE TROOP,
16TH AIR CAV, 1ST AVN BDE (AEROSCOUTS)
LOW LEVEL HELL.
'46 CJ2A
'47 CJ2A
'48 CJ2A
'48 B1PW126
'69 CJ5

Dude24578
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Posts: 5
Joined: Thu Jan 10, 2019 4:36 pm

Re: M38a1 carburetor problem

Post by Dude24578 » Fri Jan 11, 2019 2:54 pm

Thanks. I will check out the pcv system

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