Carburetor flooding

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

Post by Dude24578 » Sun Mar 10, 2019 5:01 pm

I have a 63 M38A1. For some reason I am getting too much fuel to the carburetor. When I say too much fuel, I mean that a stream of fuel flows from the vent fitting on the back of the carburetor when the vent line is disconnected. I have replaced the fuel pump with a rebuilt unit from a reputable supplier. I have replaced the carburetor from the same supplier, I thought it was the carburetor so I returned it, it was placed on a test engine and performed fine. Returned to me, installed it and it ran fine for ten minutes and the problem returned. I checked the fuel pressure while turning the engine with the starter and got a reading of 3.25lbs. I then borrowed a carburetor, installed it and it ran fine for a few minutes and then the problem happened again so I do not believe it is the carburetor, or the fuel pump. What else could it be? Thanks in advance.

novafied
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Re: Carburetor flooding

Post by novafied » Sun Mar 10, 2019 5:50 pm

hi dude, that has me stumped too. what I would do is disconnect the fuel line to the carb. gravity feed the carb with a hose and small gas can. disconnect the fuel line on the outlet side of the pump. hook up a hose to it and put in a gas can. now you can check the carb by starting it up. since it has no pressure going to it ,it won't flood out. if it runs ok, see how much gas is coming out of pump. you can add a pressure gauge to the line to check pressure. I think the engine has to be running to get true reading as you checked cranking pressure. if the pressure is good and it runs ok, it should run ok when you put back together. only the pump and float adjustment will cause it to flood out. just a thought.

KiwiMB
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Re: Carburetor flooding

Post by KiwiMB » Sun Mar 10, 2019 10:52 pm

There should be a spacer between the fuel pump and the engine block (assuming you have an original fuel/vacuum pump arrangement). Your problem is simply too much fuel pressure overcoming the ability of the float in the carb bowl to effectively control the level in the bowl. The purpose of the spacer is to lower the delivery volume of the fuel pump.

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Ian
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Jeeps4Brains
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Re: Carburetor flooding

Post by Jeeps4Brains » Mon Mar 11, 2019 8:27 am

On the inlet to the Carb, is there the brass mesh screen? That is there to filter out crud. If not in place then the crud can lodge on the needle valve that the float closes due to rising fuel in the bowl. I had the same symptoms and this was the cause.
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Re: Carburetor flooding

Post by Dude24578 » Mon Mar 11, 2019 12:47 pm

The fuel pump spacer is in place. I’m going to add a couple of gaskets to increase the clearance and hopefully reduce the pressure.

There in no screen inside the fuel line at the carburetor but I do have a fresh filter inside the fuel tank.


KiwiMB
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Re: Carburetor flooding

Post by KiwiMB » Mon Mar 11, 2019 2:04 pm

I'm not sure what fuel pressure should be, but the diaphragm spring dictates that pressure. Its possible that you have the wrong spring in place. I'm sure Ben will know the correct pressure.
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Ian
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JBizal
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Re: Carburetor flooding

Post by JBizal » Fri Mar 15, 2019 4:33 am

The screen is there. You have to remove the inlet fitting to find it.
John

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Re: Carburetor flooding

Post by Ben Dover » Fri Mar 15, 2019 6:19 am

Do you have the correct spacer?

800361 M-38/M-38A1 is 0.566"
647669 CJ-3A/CJ-5 with Vacuum booster pump is 0.112"
The WWII and CJ Jeeps with single action fuel pumps have no spacer.
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Re: Carburetor flooding

Post by Ben Dover » Fri Mar 15, 2019 10:03 pm

When's the last time you had the top off the carburetor. Can you post a pic of both sides of your engine?
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Dude24578
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Re: Carburetor flooding

Post by Dude24578 » Sun Mar 24, 2019 4:05 pm

The carburetor is a rebuilt unit from a reputable supplier. It was run on a test engine without issue. The spacer has been on the engine since the early 80s without issue until now so I assume that it is correct.

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Re: Carburetor flooding

Post by Ben Dover » Mon Mar 25, 2019 6:48 am

Have you had the top off the carburetor since it was overhauled?
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