Dear Rotaxfliers,


We own a Super Dimona with a 914F engine.

When the engine is cold, she starts perfectly.

After some towing, especially on a hot day, we encounter startingprblems within 10 till 40 minutes after shut down.

Thus: the engine starts when we start again within 5 till 10 minutes. When we wait longer the engine refuses to run. Then we wait for 40 minutes, with the cowling removed, and the engine starts again.


German collegeas told me thats a wellknown Rotaxproblem.

An engineer from Franz told us not to use the booster fuelpump. That works most of the times.

But the cause is not solved. Is there anybody who has an idea what the cause may be and how to solve it permanently?

Kind Regards from the Netherlands,

Gerard Hanstede

  • Re: Hot engine starting problem 914F

    by » 5 years ago

    In the meanwhile I know the answer. This afternoon I had a phonecall from a very kind Technician of Franz.

    He told me that when the engine is very hot and you shut of the engine that the fueltemperature in the bowls begin to rise.

    The temperature may reach as high as 90 till 100 degrees Celsius. The fuel in the bowls evaporate. Wenn you try to restart the engine after some time there will be a tremendous increase of fuelvapor in the bowls. Too much for the small rubber carb. deflate hoses. Consequence: the pressure in the bowls rises and fuel  will be injected in the carbs. Due to too much fuel in the carbs. the engine won't start.

    Solution: start without fuelpumps. The 914F has two electric fuelpumps. Disconnect the fuse of the main pump. Start the engine and after 20 seconds press the fuse of the main fuelpump to connect it to the generator. After that you may connect the auxillary pump.

    And use octane 98!


    Kind Regards,

    Gerard Hanstede.

    Thank you said by: RotaxOwner Admin

  • Re: Hot engine starting problem 914F

    by » 5 years ago

    The other thing you can do is to turn off the fuel pumps and then switch off the fuel for 30-45 seconds before shutting down - this will reduce the amount of fuel vaporization in the carbs and improve starting - it works for me.

  • Re: Hot engine starting problem 914F

    by » 5 years ago

    Fabulous good idea! I am gonna try it.


  • Re: Hot engine starting problem 914F

    by » 5 years ago

    The starting of 914F is very tricky, it shouldn't be, I am also suffering from such type of problems, mostly i succeed to start my stemme aircraft with rotax 914 F engine but with tricks. A recent experience is very intrusting , as I engage the starting key in rotary switch starter motor refuse to start, I jumped out of cock pit and turn the prope about 4 to 5 time by hand and again try for start and aircraft started and till now I am astonished how it happened.

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