Black exhaust smoke

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m38a1butch
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Black exhaust smoke

Post by m38a1butch » Mon Oct 15, 2018 8:22 pm

Recently I replaced the fuel pump which is the only thing I did prior to noticing that black smoke is coming out of the exhaust. It's not a lot while the vehicle is idling but when I depress the accelerator pedal a noticeable bunch of black smoke comes out. After noticing this I thought maybe the plugs were fouled so changed both plugs and that didn't improve anything. I can't imagine replacing the fuel pump would have caused this. I'm hoping it's not a piston ring problem. Anyway I'm open for suggestions.
USMC 1959 - 63
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1952 USMC M38A1 MD delivered 9/52
1952 1/4 Ton M100 trailer delivered 9/52
1968 USMC M274A5 (now resides in the National Vietnam War Museum in Weatherford, TX -- RIP Francis)


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Grummanflyer
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Re: Black exhaust smoke

Post by Grummanflyer » Mon Oct 15, 2018 10:03 pm

That's usually a sign of an overly rich mixture. Are you sure the choke cable is rigged properly so that the butterfly is completely open when the knob is pushed in. Make sure the return line going back to the tank is not kinked or plugged as that would overfill the carb bowl and surely cause the problem you are having.
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m38a1butch
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Re: Black exhaust smoke

Post by m38a1butch » Tue Oct 16, 2018 6:10 am

Grummanflyer wrote:
Mon Oct 15, 2018 10:03 pm
That's usually a sign of an overly rich mixture. Are you sure the choke cable is rigged properly so that the butterfly is completely open when the knob is pushed in. Make sure the return line going back to the tank is not kinked or plugged as that would overfill the carb bowl and surely cause the problem you are having.
Come to think of it, I did have to disconnect the choke cable when I replaced the fuel pump. Maybe I didn't reconnect it correctly. When I was trouble shooting the fuel pump I did blow air through the return line so unless it clogged up recently it should be ok. Thanks for your inputs.
USMC 1959 - 63
--------------------------
1952 USMC M38A1 MD delivered 9/52
1952 1/4 Ton M100 trailer delivered 9/52
1968 USMC M274A5 (now resides in the National Vietnam War Museum in Weatherford, TX -- RIP Francis)

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m38a1butch
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Re: Black exhaust smoke

Post by m38a1butch » Wed Oct 17, 2018 1:22 pm

I checked the choke and the butterfly is completely open. Any other suggestions?
USMC 1959 - 63
--------------------------
1952 USMC M38A1 MD delivered 9/52
1952 1/4 Ton M100 trailer delivered 9/52
1968 USMC M274A5 (now resides in the National Vietnam War Museum in Weatherford, TX -- RIP Francis)

muleman7
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Re: Black exhaust smoke

Post by muleman7 » Wed Oct 17, 2018 2:27 pm

1- Try idling the engine at 2400 rpms about 10-15 min making sure you have the proper oil level in the engine and lube level in the transmission. If the black smoke continues then check the carb.

2- Your carb may have a float needle that is not seating properly and allowing the fuel in the float bowl to be too high causing the over-rich mixture.

According to TM 5-2805-213-14 July 1969 pg 56 Under Descriptions and Data

The Carb Float Level [bowl inverted-free end from lip of bowl] 0.0 ti 0.093 in. [almost 3/32] above bowl flange. needle rubber tip and brass needle seat should be free of obstructions.
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m38a1butch
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Re: Black exhaust smoke

Post by m38a1butch » Wed Oct 24, 2018 2:50 pm

muleman7 wrote:
Wed Oct 17, 2018 2:27 pm
1- Try idling the engine at 2400 rpms about 10-15 min making sure you have the proper oil level in the engine and lube level in the transmission. If the black smoke continues then check the carb.

2- Your carb may have a float needle that is not seating properly and allowing the fuel in the float bowl to be too high causing the over-rich mixture.

According to TM 5-2805-213-14 July 1969 pg 56 Under Descriptions and Data

The Carb Float Level [bowl inverted-free end from lip of bowl] 0.0 ti 0.093 in. [almost 3/32] above bowl flange. needle rubber tip and brass needle seat should be free of obstructions.
What kind of tach do I use to measure the rpms ? I bought a small inductive tach but it didn't read the rpms -- maybe the tach was defective or it couldn't read through the shielded spark plug cable.
USMC 1959 - 63
--------------------------
1952 USMC M38A1 MD delivered 9/52
1952 1/4 Ton M100 trailer delivered 9/52
1968 USMC M274A5 (now resides in the National Vietnam War Museum in Weatherford, TX -- RIP Francis)

muleman7
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Re: Black exhaust smoke

Post by muleman7 » Wed Oct 24, 2018 4:05 pm

I use a SW Mechanical Tach but you can also use a Digital Tach.

SW Mechanical Tach Face View

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SW Mechanical Tach Side View

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Digital Tach

Image
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