I have a new 912uls2 that I started up for the first time couple of days ago. I did the pre-carb setup on the throttle settings backed off the idle adjustment to .004 and turned in 1.5 turns on both. Set the Idle air in all the way and then out 1.5 turns. Adjusted the throttle cables so that they both hit full throttle at same time. I have installed EGT's on all four cylinders about 3.5 inches from the flange, Now rolled aircraft out and hit boost pump to prime system and fill carbs, applied full choke and to my surprise it started on about the third blade of rotation. Idle was a little high so adjusted stops to about 1750 rpm. I bought a carb mate and had it hooked up and adjusted till I had green in middle before start. I advanced the throttle to about 4000 rpm and adjusted the cables to get even vacuum in both carbs. Now the problem is the left bank is running about 150 degrees hotter than the right and after getting the carbs sync with the carb mate, when I go full throttle only one throttle will hit the full throttle stop and the other is off about .040. The temp difference is a concern to me. Having only one carb hitting the full throttle stop be a concern when the carb mate says they are in sync? Being that this is a new engine I would think the circlip would be set right on the needles? I am really scratching my head on this. Thanks Jim
  • Re: Carb sync. EGT difference

    by » 13 years ago

    Hi James,

    Sounds like you have a cable binding issue. Many owners use too thick a cable and it doesn't allow the carb springs to work and then they have to rely on just the cables to push the carbs open and all cables will have a minute amount of play which as you have found will show up at the end with the carb arm not opening all the way. I usually tell people to not to use the plain metal sheath cable and to use the plastic lined. It is usually smoother. The all metal Bowden cable sheathing can corrode and rust then it starts to bind. Your EGT probes should be 3.93" or 100mm. If these probes aren't exactly at the same points on each side then there will be a temp spread. You are right that 150F is too wide. You need to fix those cables so the carbs work together all the way to the stop. Do not leave them like this. This would mean one side of the engine is trying to run at one rpm and the other side at another and are opposing each other. This has nothing to do with the clip.

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

  • Re: Carb sync. EGT difference

    by » 13 years ago

    I think I have the same problem James Dugan have. My Carbs are syncronized too and no vibration notice but when I put full throttle, only one carb hit the full throttle stop and the other not and I think this is why my CHT has a diference in readings too.

    My 912 is mounted on a Rans S-12. Each Carburator has its own cable that run to the throtle lever. This mean that my Throtle lever has two parallel cables, one for each carb.

    Do you think, using a spliter that have two cables for the carbs and one cable to the throttle lever will fix this issue????



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