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912ULS Soft start hard to start when warm

in 912 / 914 Technical Questions 12 years ago
Hi:
When I installed my 912ULS in My Skyranger Nynja, I connected the soft start on both ignition systems. The engine used to start OK (not great, but OK) when cold. However when the engine was warm it would take quite a lot of cranking before the engine would start and even then it seemed to be only firing on one cylinder for a while and then slowly pick up.
I have since disconnected the soft start on one of the ingitions and it seems better now. I have two specific questions
(a)Will it cause problems if I only use the soft start feature on one ignition?
(b)Should the unused soft start lead be grounded, or just left unconnected?

  • Re: 912ULS Soft start hard to start when warm

    by » 12 years ago

    Hi Scott,

    One thing that has a big influence on starting is a good carb sync, but once that is done the other major item is where the throttle is set. I.e. too much throttle, too low an idle, giving it choke after it is warm. Throttle and idle will ply a big part in warm starting. The other item that sometimes comes into play is fuel vapor or hot fuel if it has been under a hot tight cowl for 30 min. or so. I have a Rotax soft start system and don't have any issues. My idle is set at 1750, but it is never set to actually idle there while sitting. You may want to play with the throttle settings a little or check on the fuel vapor issue before disconnecting the soft start.

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

      
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  • Re: 912ULS Soft start hard to start when warm

    by » 12 years ago

    Roger:

    Thanks for that. You didn't mention whether having the soft start on only one ignition would cause any problems. I'm really wondering about long term problems in reference to this, rather than the hard starting.
      
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  • Re: 912ULS Soft start hard to start when warm

    by » 12 years ago

    Hi Scott

    It won't be a problem disconnecting one of the soft starts, although if you are turning on both mags when you start, you will be over riding the second soft start as the engine will go straight to advanced timing on one circuit while the other will still be on retarded ignition.

    If you disconnect one module, you really need to only use one mag to start, but then it won't start as good as having two soft starts as you won't be getting a good burn off one spark plug when compared to two plugs.

    If you disconnect one you may as well disconnect them both.

    You don't need to earth the power lead you are disconnecting.

    When you say the engine is like it is running on one cylinder and then picking up after a while, it is the soft start module and the new type flywheel doing its job. It will start with the timing retarded at 3 degrees AFTER TOP DEAD CENTRE, and then after between 3 and 8 seconds the ignition timing will advance to normal advanced timing of 26 degrees BTDC.

    I have the new ignition on my engine, and I think it is fantastic compared to how it used to be.

    As Roger says, make sure your carbs are balanced and your tick over is set at the right speed.

    Mark
      
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