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Thread: Carb overflowing ?

  1. #31
    4 Cycle Advanced User
    Join Date
    Jul 2015
    Posts
    140
    Quote Originally Posted by W5R View Post
    if his carb is overflowing, wouldnt that mean the seat isnt big enough to take all the fuel it is trying to feed it?
    Nope, force=pressure x area
    What your trying to control is the balance of forces between the float arm closing the needle and the fuel pressure trying to open it. Either reduce the pressure with a bypass etc or reduce the area with the correct needle and seat for the application.

  2. #32
    4 Cycle Advanced User
    Join Date
    Oct 2013
    Location
    Canada
    Posts
    888
    It would almost be the opposite off how we set pop-off pressure...
    Usually we have to get the pop off lower hence lighter spring bigger needle and seat...
    On these carbs meant for gravity feed... we are trying to raise the pop off pressure... again smaller needle and seat...

    FYI... on some FCR MX carbs the seat is pressed in... you may not be able to easlily remove it and replace...
    So much easier to keep it the same and run a dellorto pump with pressure relief built in...

  3. #33
    4 Cycle Advanced User
    Join Date
    Nov 2013
    Location
    North Carolina
    Posts
    464
    Needs a 0.7 mm needle and seat

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