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I just recent synced my carbs on my 912ULS. The aircraft is a Vans RV-12 with approximately 512 hours.


I did both a mechanical and pneumatic sync.

Two questions:

Question 1:
When I did the mechanical sync; when I moved the throttle from idle to full open, one throttle arm was fully extended and the other one had about 1/16 to 1/8 inch of play. In other words, it appears fully open until I pushed on the arm and it moved a tad more. I loosened the nut and re-tightened the nut two more times with the same results-just on the one carb. It almost appears that there is some play in the throttle arm. Is this acceptable? If not, please recommend a solution.

Question 2:

When doing the pneumatic sync, I was able to get the gauges to agree at idle (around14.5 inches) and at 2500 RPM (around 11.5 inches). However, as I moved the throttle to full power, around 3300 RPM, I was showing around 9 inches on 1 carb and around 8 on the other. As I continued to move the throttle to full power, they seemed to get in sync again and if I remember correctly at full power they were showing about 5 inches each.

Is this acceptable? I do not remember having seen this in the past, but I may have missed it.

Is there any chance the two issues are related?

Thank you for your help.
  • Re: Carburetor Sync

    by » 6 years ago


    You may have a damaged shot an/or arm most likely the shaft since it is made of brass. Have the carbs ever been overhauled?

  • Re: Carburetor Sync

    by » 6 years ago


    Yes

    Lockwood Aviation did the 200 hour inspection. They were overhauled by Leading Edge Airfoils LLC in September of 2017. They had 444 hours on the carbs at the time. I also had them do the 5 year rubber replacement as it relates to carbs at that time.

    Having said that, what you say makes sense.

    Thank you for your response.

    Bob

  • Re: Carburetor Sync

    by » 6 years ago


    I had a similar problem once where the mechanical system that split the movement from the throttle to the carburetors had a loose bearing and it made it impossible to get the carbs synced. The movement was barely detectable to the eye.

    Thank you said by: Robert J. Dean

  • Re: Carburetor Sync

    by » 6 years ago


    There are several things that may affect you carbs syncing ability. It can be the aircraft Mfg throttle linkage setup especially a dual throttle in the cockpit. Many of those are not perfect from one side to the other especially if they are connected to a long rod in the engine compartment. There is usually a slight deviation from one side vs the other. Cable setups cause issues. Sometimes too thick a cable in the cable sheath causes friction and that causes minor deviations between the carbs. When fairly new cables will stretch slightly over time and relax at different rates between the carbs. This is usually limited by time in service. Throttle cable bends is another as it may cause one or both cables to not operate smoothly.

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


  • Re: Carburetor Sync

    by » 6 years ago


    Roger,

    If this is the problem, is it something I can live with or would you recommend replacing the throttle cable or some other action?

    It is an RV-12 with a McFarlane throttle.


    Thanks,

    Bob

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