fbpx

 

Gentlemen and Ladies,

I just was completing the first annual on the Sport Cruiser and 912 ULS. Hopefully this makes sense.

On Carb Sync I was able to dial both Carbs in at 8.5 in Vac at 3500 RPM but I was unable to get the idle below 2000-2240 RPM. (Initial VAC was 9 and 6.5 at 3500 RPM and initial VAC at Idle was 19 and 6.5 with idle RPM 2000) When I did get the Idle RPM below 2000 (aggressive adjustment on the idle mixture screws) it ran pretty rough and started with a backfire etc.

The ROAN Video only shows adjustments to one carb with no mention of adjusting both carbs for Idle settings? Do I adjust both Carb idle mixture screws the same?  With both engines synced at 3500 (8.5 in Vac) at idle I am getting 13.75 and 10 on the vacuum (does this matter?). 

The videos call out for 1800-2200 RPM for Idle.  (I worry a bit about slowing the plane down with a idle RPM of 2200)

I use the throttle as the idle stop.  

Idle mixture screws are set prior to the full in and out 1.5 turns.  (adjusting these don't seem to change the idle much)

ACFT/Engine is 10 years old and has 620 hours.  Records do not document the 200 hour Carb inspection or overhaul.

What am I missing?  

  • Re: Idle Speeds and Carb Sync

    by » 6 weeks ago


    First do a mechanical sync using a .004 feeler gauge. A mechanical sync only gets you in the ballpark, but it will get you closer for your idle adjustment. I know the book says 1.5 turns in for the idle stop screw, but I find that idle too high so I only use 3/4 turn in. If your using a Vernier throttle don't use the stop plate on the carbs to stop the throttle. You will bend the idle stop screws and then the engine will quit. Install some cable stops on the throttle cables where it meets the Bowden cable adjuster.


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


    Thank you said by: Mark Keiper, WmInce, RotaxOwner Admin

  • Re: Idle Speeds and Carb Sync

    by » 6 weeks ago


    Thank you for the reply Roger.  When you say 3/4 turn your talking about 3/4 turn out after running the idle mixture screw all the way in?


  • Re: Idle Speeds and Carb Sync

    by » 6 weeks ago


    Mark Keiper wrote:

    Thank you for the reply Roger.  When you say 3/4 turn your talking about 3/4 turn out after running the idle mixture screw all the way in?

    No. The mixture screw on the bottom is turned out 1.5 turns and then leave it alone. It should never need to be messed with. It will stay put. 

    I'm talking about the idle stop screw up on top. The one you turn to make the idle higher or lower.


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


    Thank you said by: Mark Keiper

  • Re: Idle Speeds and Carb Sync

    by » 6 weeks ago


    If you are over 600 hours and have no indication that a proper carburetor inspection (involving removal and disassembly) has ever been done, I strongly suggest you get that done before you attempt anything else!


    Thank you said by: Mark Keiper

  • Re: Idle Speeds and Carb Sync

    by » 6 weeks ago


    Mark,

    The video on how to balance can be troublesome because it does not demonstrate how to address your situation. From your original post, I gather that you did all your off idle synch adjustments on one carb only and you increased the engine rpm using that carb to balance. Then you tried to lower the now too high idle using the idle speed screws. If this is correct, then this is why you are where you are and you need to start over mechanically as Roger recommends, and this time, adjust the off idle on both carbs to balance (e.g. increase rpm on one carb, decrease equally on the other). When you come back into balance, if your idle speed requires adjustment it will be minimal and you will use the idle speed screws, not the mixture screws, to raise or lower idle speed to the recommended rpm (remember to adjust both carb idle speed screws equal amounts in the same direction when doing this, make small adjustments) and you will be fine. 


    Thank you said by: Mark Keiper

You do not have permissions to reply to this topic.