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Rough idle

in 912 / 914 Technical Questions 10 years ago
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I just got my carbs back from Lockwood after a 200 hr check. Trying to finish up the annual but having problems getting the idle smooth. Mounted and Synced both carbs with synchromate but will not idle under 1900 smoothly. Looking at the EGTs they stay pretty equal but the right EGT drops rapidly below 1900 rpm 200-300 degrees. The idle mixture screws were set to 1.5 turns on both carbs. I am thinking that the idle jet is not right on the right carb. Any thoughts

Thanks

Charlie

  • Re: Rough idle

    by » 10 years ago

    Hi Charles,

    Here's a trick that I learnt from a Rotax expert. Leave your balance tube in place and connect your Carbmate up to to the manifolds using 2 x M6. See the diagram from the maintenance manual.





    Get the carbs synced with the balance tube un-clamped then clamp it and see if the balance moves (it shouldn't). If the balance moves then this is likely an indication that you have a problem with the idle circuit.

    The easiest way to unblock it is to (with the engine off) slacken the carb mounting clamp, rotate the carb so that you can access the idle mixture adjuster, wind it fully out and spray some carb cleaner directly into the adjuster hole until it comes out of the venturi.

    Reassemble the carbe (1.5 turns sounds good) and repeat the test with the Carbmate. I have found this technique to serve me well on several occasions. If the carb cleaner doesn't work you may need to find another method of clearing out the idle drillings in the venturi (which are very small and easily blocked).

    Kevin
    SyncByClamp.png (You do not have access to download this file.)
      
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  • Re: Rough idle

    by » 10 years ago

    The new balance tube rubber hose on the newer engines is longer on one side to pinch that side off. On the older engines with the equal and short hose you can't pinch it off very well. I guess I'm still old school and separate the carbs completely. I worry about a leak playing with my results in the pinch method.

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

      
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  • Re: Rough idle

    by » 10 years ago

    I agree with your the old school way Roger, plus I find it faster to remove one end of the tube compared to removing two screws, installing the nipples and the pinch clamp.
    someone needs to make a video on removing the hose from the angled fitting, its so easy if you use the right technique. (I'll try to explain: don't try to pull the hose straight off the fitting, pull the aluminum tube towards prop, bending the hose, and push on the rubber end with a blunt screwdriver. the hose is very tough so you will not damage it. hard to explain)
      
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  • Re: Rough idle

    by » 10 years ago

    I've seen people leave the adapter nipples attached all the time with rubber covers to seal them off. However if the rubber hose at the end of the balance tube is not able to take the clamp then that puts a stop to the procedure. It's a shame as it works really well.


    nipples.jpg (You do not have access to download this file.)
      
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  • Re: Rough idle

    by » 10 years ago

    Just cut the tube shorter. you will probably have to cut the hose off so plan on replacing it with some new 11mm hose of the same type.
      
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