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My 912ULS has 80 hours since new, installed in a factory built Sling 2. Starting has always been easy, cold or hot but since completing SB-912-073UL (carb circlip replacement), starting is difficult cold or hot, very rough running for about the first 5-10 seconds then it settles into normal running. All other operation appears normal. Circlips were installed in the same position as originals. As far as I know, nothing else was disturbed, has anyone else had this problem or have some information that may help me? Thanks in advance.

  • Re: 912ULS difficult start since circlip SB

    by » 3 months ago


    Check the needle position with respect to 912ULS

    And install the circlip ⭕ as per given position.

     

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  • Re: 912ULS difficult start since circlip SB

    by » 3 months ago


    Did you change the Clip with the Carb removed from the engine?
    What else may have been touched?
    Are you sure the Chokes are operating properly?  Go check them!


    Bill Hertzel
    Rotax 912is
    North Ridgeville, OH, USA
    Bill.Hertzel@Yahoo.com
    Clicking the "Thank You" is Always Appreciated.


    Thank you said by: Des Howson

  • Re: 912ULS difficult start since circlip SB

    by » 3 months ago


    Bill Hertzel wrote:

    Did you change the Clip with the Carb removed from the engine?
    What else may have been touched?
    Are you sure the Chokes are operating properly?  Go check them!

    Thanks, carbs were on the engine, will check the chokes.

    Oh, one more thing I have noticed, before start I always test the aux fuel pump (Facet) for pressure & flow. Prior to the SB, before start, pump on, flow went high then gradually reduced to zero as pressure came up and stabilised at ~ 4.3psi. Now, the flow does not reduce to zero, could I have a float problem?


  • Re: 912ULS difficult start since circlip SB

    by » 3 months ago


    Yes!  The initial flow that you see are the floats refilling the Float chamber due to fuel evaporation while parked.
    Afer a short time, the flow rate should return to Zero as the float valves conpletely close and stop the flow.
    If the float valves do not produce a total stoppage the floats will continue to over-fill and your initial start will be extremely rich.
    In operation, it is Not necessary for the float valves to completely close because there is always some flow in a running engine.
    As long as the minimum flow rate is less than the idle flow rate, the valves will be opening a little more to increase the flow.  No problem!

    Could be debris in Float valve or heavy floats.

    You could always run the AUX Pump before starting until you noticed the flow reducing and then disable the Pump. Carbs full.
    Once the enging is running the AUX Pump should be energized before the takeoff roll until reaching pattern altitude at least.
    Assuming there is not a Checklist item to disable the Aux Pump after start, you will not know if the Mechanical pump is actually working 
    until you shut OFF the AUX Pump after you are already airborn.


    Bill Hertzel
    Rotax 912is
    North Ridgeville, OH, USA
    Bill.Hertzel@Yahoo.com
    Clicking the "Thank You" is Always Appreciated.


    Thank you said by: Des Howson

  • Re: 912ULS difficult start since circlip SB

    by » 3 months ago


    Thanks Bill, yes that's what I have been thinking but hoping for a non-spanner solution, I wonder if some debris was introduced during the carb work, I'll have the LAME disassemble the carbs & take a look.

    As far as operation, my normal routine is to test the aux pump pre start as mentioned above. Start, taxi-out & run-up on the engine pump - aux on for t/off & climb then off in cruise. On again for descent, approach & landing.

    My aircraft suffers the well known (but not well understood) loss of fuel pressure issue when running on the engine pump during high power (climb) and sometimes in cruise, there seems to be no rhyme or reason for the loss of FP, sometimes it does & other times not. When the aircraft was new (up to about 20 hours ops on 95 unleaded Mogas only) it didn't display this trait, only on the first fill with 100LL Avgas did the loss of fuel pressure issue start & has persisted ever since even though I run it on 95 unleaded Mogas 99% of the time.


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