WEBER 40 DCNF COLD START/FAST IDLE MECHANISM | FerrariChat
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WEBER 40 DCNF COLD START/FAST IDLE MECHANISM

Discussion in '308/328' started by steve meltzer, Sep 30, 2025 at 4:33 PM.

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  1. steve meltzer

    steve meltzer Formula 3

    Sep 18, 2004
    1,241
    with Enzo 8995
    #1 steve meltzer, Sep 30, 2025 at 4:33 PM
    I've attached a picture of my 76 European 308 carburetor set up. There is a mechanical arm that contacts a an irregularly shaped cam like mechanism that I believe is part of the cold start and fast idle system. I'm not entirely sure how it should BE SET UP AND I'M WONDERING IF SOMEONE CAN GIVE ME SOME DIRECTION AND WHETHER OR NOT IT WOULD HAVE ANYTHING TO DO WITH SETTING UP THE SYNCHRONIZATION OF THE CARBURETORS WHEN FULLY WARMED UP. I WOULD THINK NOT, BUT I WOULD LIKE SOME EXPERT HELP.
    THANK YOU VERY MUCH

    STEVE MELTZER.
    (ADD: not sure why part of this request came out in all caps, I ain't typing it.) s
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  2. Dockboy

    Dockboy Formula Junior
    Silver Subscribed

    May 11, 2013
    631
    Maryland
    #2 Dockboy, Sep 30, 2025 at 8:41 PM
    Steve,

    It is the cold fast idle mechanism. At the bottom right of your circle, the red line passes through the adjustment screw for the cold fast idle. There is a thermostatic spring in the housing that rotates the cam as the coolant warms that in turn moves the lever and pushes on the throttle linkage.

    From your picture, it looks like you snapped it when the engine was warm as the flat side of the cam is at the lever. Also the fast idle adjustment screw at the throttle linkage is backed all the way out, so even when cold, the fast idle mechanism would not come into play.

    The way it is set now is the way it should be when synchronizing the carb throttle linkage. Once your linkage and 2 main idle stops are set correctly, you COULD crank down on the cold fast idle screw to have the function operational. Most people however disable it the way your picture shows because the cam lobe can stick and if it does, you are stuck with a fast idle.
     

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