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Hot 912ULS Won't Restart After Shutting Off

in 912 / 914 Technical Questions 6 years ago

  • Re: Hot 912ULS Won't Restart After Shutting Off

    by » 6 years ago

    The problem is neither fuel-related nor ignition-related. Note that the primary symptom is that, while attempting to start, the prop just doesn't turn fast enough. In fact, it turns unusually slow.

    I should try to hand-prop immediately after shutting off.

    The battery is new and powerful. It is located in the tail, so it's unaffected by the temperature under the cowl. Nevertheless, I should review the voltage just prior to attempting a hot restart.

    The electrical (+) line leading from the battery to the starter relay, and the (-) line from the battery to the chassis, have been checked and their connections cleaned an scoured. At first it seemed to work, but that was probably because, when tested, the engine wasn't hot enough.
      
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  • Re: Hot 912ULS Won't Restart After Shutting Off

    by » 6 years ago

    Do you have a return line installed? Your problem could be vapor lock.
      
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  • Re: Hot 912ULS Won't Restart After Shutting Off

    by » 6 years ago

    ... The battery is new and powerful. It is located in the tail... Nevertheless, I should review the voltage just prior to attempting a hot restart.

    The electrical (+) line leading from the battery to the starter relay, and the (-) line from the battery to the chassis, have been checked and their connections cleaned an scoured...


    How long are the battery Cables?
    What is the Wire Gauge?

    Also, consider that the starting solenoid may not like being Hot.

    If Possible, measure the voltage at the Starter while Cranking.

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

      
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  • Re: Hot 912ULS Won't Restart After Shutting Off

    by » 6 years ago

    Correct me if I am wrong but doesn't the soft start system allow the electrical system to fire near or at top dead center and then after the start it goes back to letting the spark advance. Is it possible the soft start isn't working when the system gets hot? Also was it doing this before you installed the new battery and the refurbished starter? Try turning on the Landing lights while starting a cold engine and watch it to see if it dims, then do the same while starting a hot engine. They shouldn't dim at all, but If it only dims with a hot engine suspect something is either drawing more current while hot or producing less current than is required. Voltage isn't everything, I am assuming you have checked the battery for cranking amps under load?
      
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  • Re: Hot 912ULS Won't Restart After Shutting Off

    by » 6 years ago

    I think Bill may be onto it. Cranking speed with a new battery should be fast. One common problem with low cranking speed is resistance on the contacts of your starting solenoid.
    It is an easy test to place a meter (preferably an analogue one as you can see the needle move quickly) with the positive lead of the meter on the cable going to the battery (these are the large bolts on your solenoid) and the negative lead of your meter going to the starter lead. In this configuration you should see the full battery voltage displayed on your meter. You then need to get an assistant to crank your engine. This will energise the starter solenoid causing the engine crank to rotate and your voltage reading should drop to somewhere below a volt. This means that all of the current is being fed into the starter and not being lost as heat due to contact resistance within the solenoid. You will be reading the voltage drop across the solenoid.

    Regards........Chook.
      
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