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I found 5 years old correspondence relating to the issue, however, I'm not sure if the McFarlane carburetor springs issue is settled.

I own a Tecnam P92 Echo Classic Deluxe with a Rotax 912ULS engine and a Tecnam made friction mechanism (for both parallel throttles). The mechanism is pretty inefficient in keeping the throttle fixed and we experience throttle runoff at critical flying stages, mainly landing. we already replaced the mechanism parts once.

We consider replacing the carb springs with McFarlane softer 6822 and 7235 springs, however would like to have a Rotax confirmation to their compatibility.

I would love to have Rotax formal reference to the issue, and any other references from the forum members.

  • Re: McFarlane carb springs

    by » 6 weeks ago


    I know that some owners have fitted these in the UK:

    https://www.lasaero.com/products/article/W00WYPOZB

    The original Rotax springs are very strong and our throttle friction has to be very tight which I do not like.


  • Re: McFarlane carb springs

    by » 6 weeks ago


    Vans RV12's have throttle creep issues. They did go to better throttle from McFarlane and went to lighter springs from them. Replacing the parts on the throttle you have won't help. You would need to use an upgraded and better throttle from them. They do have them as I have installed a few of them. The friction lock is far better. You can use lighter springs and they seem to work. If springs get too light and depending on the throttle mechanism it can make carb sync a PITA because the lighter springs don't do as good a job pulling the throttle levers on the carbs all the way open on both carbs each time you cycle the throttle..


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


  • Re: McFarlane carb springs

    by » 6 weeks ago


    Rotax will not provide you with a formal reference to the issue or confirm their compatibility. Rotax will only provide you with the Service Letter - Non-Approved Modifications or Unapproved Engine Components or Accessories document that you can find here. - https://legacy.rotaxowner.com/si_tb_info/serviceletter/sl-912i-005.pdf

    You will need written permission from Tecnam to make any changes to the aircraft including changing the strength of the throttle springs OR the relocation of the throttle springs to be "legal"

    The throttle springs are positioned (from the Rotax factory) so that in the event of a throttle cable breakage, it will go to full power (WOT) . Some aircraft manufacturers change the position of this throttle spring to go to full ide in the event of cable breakage and some remove the spring entirely.

    It is up to the manufacture of the aircraft to decide how they should have the throttle springs configured and designed so that the throttle works properly and can handle the strength of the throttle spring of the carburetors. 

    Unfortunately, this is an issue you need to take up with Tecnam and seek their approval for modification. 


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