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Thread: OS 75ax help


  1. #1

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    OS 75ax help

    got a new 75ax, i have ran 2 tanks of fuel on stand. put on plane ran 1 more tank on rich side, lean engine out and flew 2 more tanks. it is slobering all over the place, after last flight i stood over plane to hold it in place and my legs and shoes was covered with fuel. it is about as lean as I want to go on a new engine. no body at our club has had this engine, one member said to rich up the mixture screw so i could lean out the needle screw more. the instructions are not much good for this.

  2. #2

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    RE: OS 75ax help

    G'day Mate,
    Sounds like it is too rich, here's what I do, first you need to find your tuning range.
    I always use an extension on my needle valves, just a piece of wire, with a circle bent on one end & a flat filed on the other,
    put into the needle valve, & tighten the grub screw, it's usually a 2 mm grub screw, & the Allen key comes with the engine.
    Start the engine, & at full throttle, very slowly wind the main needle in, until the revs start to drop, this is your leanest point, note the position of the wire circle, on the needle valve extension.
    From there wind the needle back out & note when the revs start to drop, this is the rich point of your tuning range. Now you know the tuning range of the engine,
    just wind the main needle in, about 3 to 5 clicks, hold the plane vertically, & the engine should speed up slightly, meaning it is rich enough, it is now ready to fly.
    The tuning range will vary depending on fuel, ie amount of nitro, more nitro, wider tuning range, prop, temperature, altitude, & other variables.
    But whatever you do, don't be tempted to lean it any more than those few clicks.

    Cheers.
    Good Flyin Mate. Keep Thyne Airspeed up, lest the ground arise & smite thee,
    Allan.

  3. #3

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    RE: OS 75ax help

    yea I know how to set the high speed needle but there is somthing new to me about the carb mixture screw (not high speed) on the ax engine carb.

  4. #4

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    RE: OS 75ax help

    Hi!
    What's new? The low spéed needle works as on any other two needle carb.
    In for leaner and out for richer.
    Jan Karlsson - Supplier MVVS Products


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