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My 912 S started to kick back during startup. The problem has been increasing until it was impossible to start in the end.
To improve starting I balansed the carburators and installed the Heavy Dutu starter from Sky-tec.
To solve the problem I installed the soft starter module (no improvement)
Then we overhauled the carburators with new jets and new needles.
I have to change the spragcluch which is damaged because of the kick-backs.
Now I have been recomended to change the freewheel with a new type that gives a later ignition timing.
But, will this work? Anyone experienced the same problem? :(
  • Re: Hard start 100 HP 912

    by » 14 years ago


    Sounds like your on the right path. Since you have done a few of the other items here would be my best guess. I am assuming you have a good battery. I would wager that pulling the gearbox, replacing the bellville washers and re-shimming to bring up the friction torque to 460-500 in/lbs will solve the kickback issue.
    Keep us informed.

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


    Thank you said by: Kjetil Kristensen

  • Re: Hard start 100 HP 912

    by » 14 years ago


    I know how you feel. Mine kicks back as well. I balanced the carbs and got a really strong battery. Each time I start it now I tap the starter a few times before starting it. It is much better in the summer than winter. I pre-heat the engine in winter and that really helps as well.
    Dennis

  • Re: Hard start 100 HP 912

    by » 14 years ago


    Kjetil

    Did you say you already changed the sprag clutch or still have too? A bad sprag clutch will lead to excess kick back as it slips during start up allowing the higher compression of the 912ULS to resist cranking over effectively!

  • Re: Hard start 100 HP 912

    by » 13 years ago


    New sprag-cluch and freewheelhub with new ignition timing is on the way. Setting me back 1000 Euros. I also previous bought a new starter, soft start module, new jets and needles pluss manhours and redused flying.

    From reading different forums this is a common problem with the 912 100 HP. It is a shame that Rotax won't take responsibility for this tecknical problem as they did with the gearproblem. :angry:

    Rotax have developed new Freewheelhub and new ignitionmodules to repair this tecknical problem... And we have to pay!

  • Re: Hard start 100 HP 912

    by » 13 years ago


    About 2 years ago the Soft Start totally stopped my kickbacks which plagued me for the previous 6 years
    I changed the sprague clutch and housing which did nothing and could see no damage to the old one.
    Understanding the problem now, I think it is a problem of not enough torque on the gearbox and too much ignition advance too soon in the starting process. Rotax had no answers for me. Everyone else had answers like: smaller plug gap, harder engine mount rubbers, bad battery, bad fuel, etc. etc.
    It is difficult to get help on a Rotax because of so few of them around compared to Lycoming or Continental engines and Rotax manuals are very vague and the English is poor. Buy a Honda manual or Suzuki manual and the difference is quite obvious. Rotax has a long way to go. Do I think it is the best engine out there? It is the very best without a doubt even with the highly inflated prices, it is the best.
    Dale

    Thank you said by: jaap wijsman

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