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Hi all, The temperatures been up in the 90s here in the Midwest and The sting was sitting for about two weeks in the hanger which could've been hotter? I went to start , did the normal Mags on Main on aux fuel pump on until I heard the line charge , aux pump off, choked -throttle back . 10 or 15 seconds went by nothing , removed choke and give it a little fuel , try ed again. about the same, let it set for a few minutes, and tried again with no choke a bit more fuel it finally fired and was very rough kind of seemed flooded .
Since then been reviewing my /the starting procedures And analyzing what could've happened ? This is my first hot summer with the plane so I believe it has something to do with temperature , once she started everything was normal from that point on for the flight . About a week later I had the same situation almost identical so I thought I would come back the very next day and try again . Did a bit of research at this point ? Plugs fouled, carb sync, fuel, battery issue? , The plugs were new, just had an annual recently, and battery is always on a tender and checked it for voltage and it was fine.
So anyway the following day I read somewhere to put the aux pump on for 10 to 20 seconds so it usually takes 5 to06 seconds for it to sound like it was charged, this is been normal but I came out of a cold season cold starts. I kept it on for 10+ seconds and it seem to start much better do you think this could be a fuel evaporation issue really starting procedures for when it's hot would be helpful thank you. PS I plan on pulling all the plugs and making sure they're not fouled!

I was waiting for my silicone heat sink compound from California power systems .
  • Re: Hard starting

    by » 7 years ago


    PS can you flood the engine by having the aux pump on too long I was always taught to just charge the line until you hear those sound change? Thank you have a great Fourth of July ! Blessings

  • Re: Hard starting

    by » 7 years ago


    The possibility exist, but if the carbs are functioning right they shouldn't.

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


    Thank you said by: John Wilfley

  • Re: Hard starting

    by » 7 years ago


    Thx Roger, question does the aux pump just fill the bowls, and then go to.the return line back to tank, trying to understand the function as how its operated and is used. Is it like a carb primer or does pressurize the system.

  • Re: Hard starting

    by » 7 years ago


    The possibility exists, but if the carbs are functioning right they shouldn't.


    Roger is correct!

    You should be able to leave the Aux pump ON for the entire flight if you wished.
    It is not uncommon to operate the Aux pump whenever you are At or Below pattern altitude.
    It will keep the mechanical pump primed and ready for a quick restart when really needed.
    It also prevents any vapor lock from forming on final approach due to the combination of a slow fuel flow rate over a Hot Engine with slow airflow.

    Once the carbs are full, the float valves will close and stop any more fuel from entering.

    What kind of pump do you have?

    A motor driven pump may change sounds as it acquires its prime.
    That does not mean the carbs are full.
    Once the carbs are full the pump will either bypass or just spin pumping nothing.

    A solenoid type pump will slow down slightly once it gets its prime.
    Again, the carbs are just starting to fill at this point.
    Once the carbs stop accepting any more fuel, the "Clicking" will stop or click occasionally once it reaches its cutout pressure.

    There is no reason to shut OFF the Aux pump during startup.
    Move the "Aux Pump ON" instruction, a few more steps up the checklist.
    By the time you get to "Clear!", The carbs should be full.

    Bill Hertzel
    Rotax 912is
    North Ridgeville, OH, USA
    Clicking the "Thank You" is Always Appreciated by Everyone.


  • Re: Hard starting

    by » 7 years ago


    At these temperatures (here we have 95+) we do not use chocke at all. The engine fires immediately and runs smooth. The aux pump shouldn't be able to flood the carbs. But I have noticed that if we chocke the engine with so high temps, the engine runs rough after start up.

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