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Thread: Fuel leak-down m38a1

  1. #1
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    Fuel leak-down m38a1

    After having my fuel tank cleaned and coated, and my military two-stage fuel pump rebuilt,and after installing an online fuel filter, my Jeep starts and idles/ runs well for awhile. But after awhile it starts to act starved of fuel and dies. Then the fuel visible in the inline fuel filter bleeds back down. Any thoughts on why? All help greatly appreciated. Thanks David

  2. #2
    Super Moderator bmorgil's Avatar
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    A little more info David. Does it start and idle for a while and then die? Or, does it run fine down the road and suddenly start acting up? When you say it is starving for fuel, does it stall when you try to give it gas? As long as you see fuel in the filter things are good. It doesn't need to be full. It may drain back when it is shut down, but it should take a while. The pump should only allow flow in one direction.
    Last edited by bmorgil; 03-15-2021 at 06:42 AM.

  3. #3
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    The first time it was started after the above work, it was run only in the garage. After @ 8-10 minutes it started to die like it was running out of gas... I then started it again and stood beside it to observe. Being warm, it didn't take as long to act as if it was running out of gas and this time I observed that the gas appeared to be flowing backwards out of the inline fuel filter, which it in fact was. Then I checked the fuel line connections and started it up and drove it around 3 miles, as long as I pulled a little throttle it ran long enough to get it back to the garage. Then when I pushed the throttle back in it died again. I'm coming to the conclusion that the rebuild on the fuel pump was done incorrectly and I'm going to replace it with a glass bowl fuel pump next.

  4. #4
    Super Moderator bmorgil's Avatar
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    David when you say "you pulled a little throttle" are you saying you are choking it? Can you keep it running by choking it, pulling the choke knob? Or are you saying if you keep your foot on the gas or pull the "Throttle Stop knob" it will stay running?

  5. #5
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    Sorry,meant choke. Wouldn't stay running regardless.

  6. #6
    Super Moderator bmorgil's Avatar
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    There's probably junk in the idle circuit. It seems like its "Carter carburetor clog the idle jet week", someone else is having a similar issue. One of the most sensitive areas on those carter Carter YS-950's and all the similar Carters on all the Willys, is the idle circuit. The idle jet "Nozzle" plugs up by suggestion. If it will run with the choke but not without, and it will run at high rpm 2000 or so (Throttle opened up a bit), the idle circuit is most likely clogged. When cleaning it out don't be surprised if you find nothing. The blockage can be minuscule. Blow high pressure air through everything. You absolutely must pass a wire through all the jets and "Nozzles" whether they are new or used. It is the only way to insure it isn't corroded shut. I have pulled enough Nozzle jets right out of the package, to find them corroded shut with microscopic corrosion. These Carters were used on a lot of things. On the Carter YS-950 there is the addition of the vacuum accelerator circuit. On a Carter YS-950 there is not an accelerator pump assist until there is engine vacuum. A vacuum leak in this circuit will cause similar problems with idle quality, but in addition the engine will stall if you try to give it any throttle rapidly. I think you are going to have to clear out the carb passages. Let us know how it goes.
    Last edited by bmorgil; 03-16-2021 at 12:01 PM.

  7. #7
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    Thanks for the help, I've got a spare carb and am going to send it to be rebuilt. Will let you know.

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