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Several weeks ago I dismounted my 912ULS engine and sent it to a reputable Rotax repair shop in Arlington, WA to have a cracked ignition housing replaced. They also serviced my 850 hour gearbox and put in kits and sockets in both carbs. I got the engine back and finished remounting it yesterday with all new hoses (5 year rubber replacement, actually 7 years). Did the oil purge and then tried to start it-no joy.

It cranks over just fine but no hint whatsoever of firing. The battery is strong and fully charged, oil pressure comes up immediately, fuel pressure is 4 psi, voltage is all good. It is getting fuel; I dropped the float bowls and they have fuel and the floats are fine and weigh correctly. I traced out all the wiring that had been disturbed and put an ohmmeter on the ignition pins at the module plugs to make sure they were not grounding out when the keyswitch was in the BOTH and START positions. Fully recharged the battery several times and tried to start it, but no ignition whatsoever. I also tried using starting fluid in case the carbs were messed up or the fuel was about a month old, but no improvement at all. 

I am at a loss as to what to do next. Hopefully I don't need to dismount the engine again in order to inspect the new ignition housing. The 4 little trigger do-dads mounted on the back appear to be solidly in place. This engine has been running perfectly for 850 hours before I sent it out for the ignition housing replacement.

  • Re: 912ULS Won't Start

    by » 4 months ago


    I'm not going to be much help James, but FWIW on another thread here I just got some education from Bill regarding the spacing gap of those trigger coils ("4 little trigger do-dads mounted on the back appear to be solidly in place.") In short they not only have to be solidly in place but gapped right. 

    I would assume/hope that the reputable shop didn't even touch those gaps, but if it's easy to check you might do that. Bill states the correct gap is ~0.4mm. Are they...the gaps... reachable?


  • Re: 912ULS Won't Start

    by » 4 months ago


     Throttle and choke positions?


  • Re: 912ULS Won't Start

    by » 4 months ago


    The trigger coil gaps are not accessible with the engine mounted. I talked to the shop that replaced the ignition housing and he said they set the gaps properly. Throttle set at idle and choke fully ON, which is the way I always did it before. After no luck, I did try some other combinations.

    I want to check if there is spark at the plugs. was planning to remove a couple of plugs, with wire attached, plug threads grounded against engine case, then turn it over with the starter and observe if a good spark occurs. Is there any harm in doing this to the ignition system??


  • Re: 912ULS Won't Start

    by » 4 months ago


    Pull one plug each on a front and rear cylinder and do the hanging spark plug test.  No Harm!

    Pull the 6-Pin connectors apart and re-seat them, they may not be fully seated.

    And confirm the correct pairs are plugged together.  There are 24 ways they can go together, 23 of them are wrong!

    Confirm the 2 Ground (Black) wires coming from two of the 6-Pin Connectors were Re-Grounded.

    - - -

    And by "Ignition Housing", you mean that $1700 block of aluminum that makes up the whole back end of the engine. ???

    The trigger coils spent at least a few minutes lying on a table before they were transfered into the new housiing and realigned.

    This means that EVERYTHING related to spark generation is now suspect.


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


  • Re: 912ULS Won't Start

    by » 4 months ago


    Thanks Bill, will do. Yes, the aluminum ignition housing was cracked. There was no new replacement in the US, so I opted for a $1400 used one that had been completely overhauled (yellow tagged) by an authorized Rotax rebuild center, with new water pump seals and new crankshaft bearing and seal. I agree, everything back there is now suspect. 

    If your suggestions, which I will do, do not help, what do you suggest I do then? Completely dismount the engine again and ship it back to the shop in Arlington, WA that did the work? I feel plenty qualified to mount and dismount the engine and do all the hookups, but I don't feel qualified to inspect and repair the ignition system. I am resisting pulling the engine again due to all the work involved, two days to get it unhooked and dismounted, then 3 days to remount and hook up everything. Pulling off hoses that have been tightly clamped to barbed fittings is a REAL pain. 


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