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S83P carb rebuild leaking fuel

Discussion in 'Daihatsu Hi jet' started by bohale87, Sep 18, 2021.

  1. bohale87

    bohale87 New Member

    Got it all back together and fired up after a couple turnovers, idles decent for not being adjusted.
    A couple things, firstly when you rev it up, it has good response but then when it idles back down it kicks back up in higher rpm.

    Secondly, when you shut it off there is fuel coming from the Venturi? No fuel leaking on idle, only notice dripping out of it after cutting the machine off. See picture circle in blue is where it drips from.
     

    Attached Files:

  2. Jigs-n-fixtures

    Jigs-n-fixtures Well-Known Member

    That indicates that the fuel bowl is overfilling. A few possible causes:

    1.) The float is misadjusted. The float should be parallel to the top of the carb, when the top is inverted, and the float is resting on the needle.

    2.) The needle and seat are bad.

    3.) Something is over pressurizing the inlet line. You should have about 2-psi, at the carburetor.
     
  3. bohale87

    bohale87 New Member

    What do you mean over pressuring the inlet. The inlet is fed from mechanical fuel pump so I can’t see it being that. The spec calls for .575” top of float to top of housing when inverted, got that set, this is a new rebuild kit with needle and seat so it’s hard to believe that’s it. I guess I’ll take carb off again and clean seat and needle
     
  4. Jigs-n-fixtures

    Jigs-n-fixtures Well-Known Member

    Check the fuel pressure. Just tee in a pressure gage, and check the fuel pressure after you run it, and things are warmed up. When it is flowing out of the bowl into the venturi, open the gas cap. Does it suck in or blow out?

    A frequent problem is that the charcoal canister goes bad. That prevents the tank from venting correctly. That builds pressure in the tank. The fuel pump regulates the outlet pressure by dumping pressure to the return line. With the tank pressurized, the pressure from the pump has to increase by however much pressure is in the tank. So, if the tank has 2-psi of pressure, and the pressure relief valve in the fuel pump which controls the discharge pressure is designed for 2-psi, then the pressure to the carb will be 4-psi, and it will flow right past the needle and seat. That overflows the carburetor bowl, and dumps into the Venturi just like our picture shows. And, the engine is now so flooded it is really hard to restart.

    This is an example of the gauge I’m thinking of. https://www.amazon.com/Fuel-Vacuum-...el+pressure+test+gauge&qid=1633572054&sr=8-44
     
    Last edited: Oct 6, 2021
  5. bohale87

    bohale87 New Member

    Check the gas tank to suck in or blow out?
    is there a way to check charcoal canister?
    would it be easier to split in a fuel pressure regulator before the mechanical pump or I guess that won’t matter if not venting properly?
     
  6. Jigs-n-fixtures

    Jigs-n-fixtures Well-Known Member

    On mine, I went with filter and an electric pump back at the tank, and a second filter, and pressure regulator just before the carb, and blocked the fuel return line. I really should have tried to rehab or replace the charcoal canister. But, since mine is a “pick/tipper”, it was very easy to raise the bed and get at the fuel tank, and the engine. So, the brute force electric pump and regulator is what I went with.

    There are videos on YouTube on rebuilding the charcoal cannisters. Basically, you need some activated charcoal, and some fiberglass filter media. Both, can be bought at an aquarium supply, or pet shop.
     

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