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We have a weird problem starting our 914 when the ambient temperature is very cold. It's as if it starts on only 2 cylinders and will not pick up from there no matter what you do with the throttle or choke - you have to switch off and try again and sometimes it eventually goes. Once the engine starts properly it runs sweetly and starts subsequently with no problem.

Here is a video of what it sounds like.

https://drive.google.com/file/d/1XfjrbyZekuK_U98ipVAIaG7FH1QmsCUe/view?usp=sharing

It does this whether trying to start with both or just A or just B ignition circuits live. We know when it is running per the video it is actually firing on all cylinders as we have checked the exhaust temperatures with an infra-red thermometer.

We replaced the ignition modules with brand new units and swapped both carbs with spares and the problem persists.

As changing the carbs made no difference it looks like it must be an ignition problem. We heard the ignition coils never go bad, so guess it must be something to do with the charging coils, trigger coils or wiring.

Any suggestions as to what to do next ?

Thanks, Mark

 

  • Re: 914 Won't Start Properly When Cold

    by » 4 months ago


    I am assuming you know that rotax choke system is different. The throttle must be closed or it will not function as intended. After engine starts you can disengage choke and apply throttle to warm up rpm. 

    During none cold start, the engine will stop if choke is applied. You start second time without choke indicating you did not need choke that day but used choke just to confirm none was needed. Either case throttle if adjusted properly should always be at closed position if choke is applied.

    I don't know if rotax like lycoming or continental aircraft engines has a cold temperature recommended preheat procedure. Lycoming recommends preheating engine if ambient temperature is 10 degrees F or below and continental 20 degrees F and below. 

    You did not mention what ambient temp was. Have you tried preheating engine before start if it's really cold and see how things perform. Sometimes moisture gets between some spark plug gaps and freezes. 

    I don't fly my gyrocopter with 912 below 50 F since its open and I have no heat. I have another aircraft with lycoming engine and I do preheat before start if it's below 40 F. 

     

     


  • Re: 914 Won't Start Properly When Cold

    by » 4 months ago


    Which 2 cylinders are cold???
    Front vs Rear = Electrical Issue.
    Left vs Right = Fuel Issue.

     


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


  • Re: 914 Won't Start Properly When Cold

    by » 4 months ago


    None are cold - it sounds like its only running on 2 cylinders but that isn't the case as all are hot as measured with infra-red thermometer


  • Re: 914 Won't Start Properly When Cold

    by » 4 months ago


     

     Yes we have the throttle fully closed when using the choke. It doesn’t need to be that cold for the problem to happen – around 40 Fahrenheit/ 5 Celsius.

     

    Warming the engine does help (we initially thought it was the ignition modules as warming them seemed to solve the issue, but I think it was just the general warming of the engine bay that did it).

     

    The previous engine we had, did not have this problem so it’s very strange !

     

    Thanks, Mark

     


  • Re: 914 Won't Start Properly When Cold

    by » 4 months ago


    Sorry!  I misread your 2 cylinder comment.
    Assuming it is only on the first start of the day,  How long since the previous flight?
    Are the electric fuel pumps running for any significant time before the first start attempt?

     


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


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