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Engine Idle Mixture Setting

in General Tech Discussion 11 years ago
I am unhappy with the carb syncro I did at 20 hours and I feel that my 912 just runs a bit rougher than it should. I bought the sync dual gauge kit from Lockwood and plan on giving it another go with a second set of eyes (Dad). I am at 6200' MSL here in Colorado. Since I find that the rough running engine usually happens at 1725-2000 RPM should I try to reset the idle mixture screws to 1.5 turns? Would a slightly more lean setting be better?
Any other advise on getting the carbs dialed in really good? This PPC sat for 9 months. I am considering, after talking with Lockwood pulling the idle jets out and making sure they look clean of varnish although I have found no varnish anywhere else including in the bowls. Thanks for your help.
Matt

  • Re: Engine Idle Mixture Setting

    by » 11 years ago

    Hi Matt,

    Good question.
    How many TTSN hours on the engine and when was it built? This may play a small role here depending on your answer.

    Since it sat for 6 months I would pull the carbs and just flush them with some spray carb cleaner followed by some air pressure in all orifices. When flushing or using air pressure make sure the piston or slide is out of the carb and the top off. The idle jet hole is very tiny and will clog easily from old fuel or debris. You should be able to hold it up to the light and see light through it. You can go through the carb sync now then have to pull them anyway and then sync them again or just pull them now and have a good one time sync and save all the time. To give you an idea of how small the idle jet hole is I usually take a 16 ga. wire and strip it back then I peel off one strand of that wire to fit into the hole of the jet to clean it out. Flushing fluid alone won't do a great job. Remove the idle mixture screw too and flush through it. Once done you should have no issues syncing at idle. A bowl inspection if it hasn't been done in a while is warranted here anyway. I would leave the idle mixture screw set at 1.5 turns as it states in the book for now. If need be you can tweak it later for your elevation.

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

      
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  • Re: Engine Idle Mixture Setting

    by » 11 years ago

    Roger,
    Thank you for your help. I really appreciate it. 31 total hours and build in 2010. I'm a little nervous about getting the carbs set back up right after pulling them. Are they generally way out of wack when you reconnect the cable linkage? Sounds like it would be a good idea to go ahead and clean them up.
      
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  • Re: Engine Idle Mixture Setting

    by » 11 years ago

    You don't have to disconnect the throttle cable. Just remove the 11 mm nut on the throttle arm and spring and slide it off and leave the cable untouched. Remove the choke spring and undue the choke cable at the screw attachment point. Then remove the two screws on top of the carb and slide the carb dome off and remove the slide. The cables will stay with the top of the carb. Now the carb will come off without ever having to re-adjust the throttle cable.

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

    Thank you said by: Matt Wassam
      
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  • Re: Engine Idle Mixture Setting

    by » 11 years ago

    Matt,

    Take the top and the choke lever off the carb and leave the cables attached. You can then remove the carb without changing any cable settings. When you replace the carbs, your carb sync will be very close to where it was before. Just possibly a little tweaking with the sync will put you back in business.

    Bill.
    Thank you said by: Matt Wassam
      
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  • Re: Engine Idle Mixture Setting

    by » 11 years ago

    Thank you gentlemen so much for your help. I will pull them off and get them cleaned up. Thank you again. This is so very helpful. Matt
      
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