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Info Pilot/Mixture Screw

Discussion in 'Yamaha 250cc In-Line 4's' started by ROVER LARRAGUIBEL, Jun 27, 2021.

  1. ROVER LARRAGUIBEL

    ROVER LARRAGUIBEL Active Member

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    Hi friends...

    I have a question about the operation of the mixing screw.
    BDST_PilotScrewFitted.jpg

    What is the function of this screw?
    Will it be to increase or decrease the air in the mix?
    Will it be to increase or decrease the fuel in the mix?
    Will it be to increase or decrease the mixture itself in the cylinder?

    Currently I have the screw with three turns out ... and the spark plugs are soaked with gasoline.

    Thanks
     
  2. maelstrom

    maelstrom LiteTek Staff Member Premium Member 250cc Vendor Contributing Member

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    • Although mostly referred to as a fuel screw (including by me), it is actually a fuel-air screw. It is used to set the idle mixture and also overlaps off-idle.
    • Screwing it out creates a richer mixture.
    • Air enters via the pilot air circuit in the mouth of the carb, and many carbs have a removable air jet. It then mixes with fuel drawn via the pilot jet.
    • The main and pilot jet look identical and it is easy to mix them up.
    • The 'n' turns out should be considered a starting point only. See https://litetek.co/Guide_FuelScrews.html
     
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    Last edited: Jun 27, 2021
  3. GreyImport

    GreyImport Administrator Staff Member The Chief Contributing Member

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    And it should be setup like this ....

    PilotScrewAssy.jpg
     
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  4. maelstrom

    maelstrom LiteTek Staff Member Premium Member 250cc Vendor Contributing Member

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    If you are seeing large amounts of excess fuel then
    • check that your float needles are in good condition and both assembled and sealing correctly.
    • check fuel level see this guide https://litetek.co/Guide_Mikuni_BDST_Fuel_Level.html
    • Check that the fuel pump is functioning correctly and is a low pressure pump as per OEM
     
  5. ROVER LARRAGUIBEL

    ROVER LARRAGUIBEL Active Member

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    Thanks!!!!
     
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