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Carb sync for beginners

in 912 / 914 Technical Questions 10 years ago

  • Re: Carb sync for beginners

    by » 10 years ago

    Don't sync them at low rpms on the high rpm setup. Sync them at idle and then at approximately 3500. Do the high sync first as it may throw the idle off some if you have to adjust the cables at the adjuster. The 2000-2500 rpm is too close to idle and won't give you a good sync for higher rpms and that's why you have the difference. If you sync them at 2000 rpm then as you advance up to higher rpms like 3500 the vacuum will differ again. There is just too little air/fuel flow at low rpms (2000) to be any help at setting the system up for higher rpm use. Carbs are rarely perfect vacuum as you advance up out of the idle circuit, but tend to do better as the rpms increase. You don't fly down at 2000-2500 rpm either. Sync them up higher at 3500 rpm and they will have a better sync as the rpms climb. Don't worry about the vacuum between idle and 3500. It is what it is. The balance tube will help compensate for some of this too. The carbs may not be as smooth separated as they will be with the balance tube reconnected. If I want an 1800 rpm for idle I set them at about 1750 or so while the carbs are separated because when the balance tube gets reconnected it tends to raise the idle rpm just a tad.

    Set them up at idle and around 3500 rpm and leave the rest alone.

    Roger Lee
    LSRM-A & Rotax Instructor & Rotax IRC
    Tucson, AZ Ryan Airfield (KRYN)
    520-349-7056 Cell

      
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  • Re: Carb sync for beginners

    by » 10 years ago

    Ok, I made 3500 sync and then idle by screws. It wasn't working good until balancing tube fitted. Now it's great.
    Thanks.
      
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  • Re: Carb sync for beginners

    by » 10 years ago

    Glad it worked out okay.
    Anytime you have the balance tube disconnected the carbs will be a little rougher even with the carbs in sync. Once the tube is hooked back up it should be nice and smooth. If you have an engine with rubber engine mounts over 5 years old and the carbs are synced and it seems the engine still shakes a bit in the mount (may be interpreted as a rough running engine) then it may be time to replace or take a hard look at the rubber engine mounts. Also remember to not set the idle too low which is even more important for the 912ULS with its higher compression over the 912UL.

    Once the carb sync is done then doing it at every 100 hrs. or the annual should be really easy and only need a little tweak. Rarely will they stay perfect by the end of 100 hrs. or an annual. It does happen, but not very often so they should always be checked at these two markers or if something strange pops up somewhere in between. It can become a diagnostic tool if need be.

    Roger Lee
    LSRM-A & Rotax Instructor & Rotax IRC
    Tucson, AZ Ryan Airfield (KRYN)
    520-349-7056 Cell

      
    Report

  • Re: Carb sync for beginners

    by » 10 years ago

    Hi. I was checking my spark plugs yesterday. It's the problem with spark plugs color. 1 and 3 cylinder plugs (left) have nice colorized plugs but right (2,4) have a little bit dark (to rich). I suspect my right carb gives too rich mixture.
    I have carbs synchronized on 3500RPM and it's working good. On Idle (1700rpm) i set vacumms by stop screws but on 2200, 2400 engine runs rought...
    I thinking about screw in mixture screw a little bit (I don't know how much) and re-sync them again.
    It is good idea?

    If I good understand I should screw in screw number 51.

    Zrzutekranu2014-10-15o10.19.33.png (You do not have access to download this file.)
      
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  • Re: Carb sync for beginners

    by » 10 years ago

    I'm not sure. I should to tune by screw number 7 o jet needle position?
    I can read:
    "Improper Fuel / Air ratio.

    The Fuel / Air mixture in the mid range is adjustable by moving the jet needle up or down, allowing more or less fuel into the carburetor."

    Can I set jet needles on different positions on each carbs?
      
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