Good afternoon everybody

Maybe this problem was already discussed before but I couldn ´t find a topic.
Engine: 912UL 80hp, New spark plugs, Compression ok, etc.

During Run Up on ground Ignition circuit -B- delivers a very rough engine run below ~3000rpm.
Above ~3000rpm Circuit -B- is running fine (rpm drop at 3800 approx 150rpm)
Ignition Circuit -A- is always good.
In Flight Circuit -B- shows a fall back into it´s bad behavior on ground during all rpm-ranges
(Very rough engine run with a loss of >500rpm)

First I suspected Circuit -B- running on 3 sparks only but this was not confirmed.
(I pulled all -B- sparks one by one and grounded the plug concerned with a dummy-spark-plug.
Result: the engine run was even rougher. I even tested all -B- sparks with a colortune tool)

Next investigation step was to swap the trigger-coil plugs in order to find out that the trouble
moved to the -A- Circuit. Therefore I assume the electronic modules and coils to be ok.

Hence I suspect the -B- sparks to be too weak or their ignition timing slipped behind -A- ??

Then i grabed my old multimeter and tested the trigger-coils.
The resistance on all 4 ´channels´ is fine (4x 230 Ohm)

Next step will be to verify the small gap between the rotating part and the trigger coils
(0,3mm approx)

Any idea somebody in this community?

  • Re: Ignition Circuit -B- Problems

    by » 7 years ago

    Hello Gerhard,
    I have exactly the same problem with the same model engine and it's driving me nuts. I've been through the same tests you've performed and gotten the same results. Were you able to determine what was/is causing the issue? I didn't see any replies or further posts on this issue. Thanks and best wishes.

  • Re: Ignition Circuit -B- Problems

    by » 7 years ago

    We never heard back if he found his solution.

    I would have changed all the spark plugs and failing his other test would have checked the trigger coil gaps on the back of the engine.

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

    Thank you said by: Tom Mandell

  • Re: Ignition Circuit -B- Problems

    by » 7 years ago

    Thank you Roger for your reply and feedback. If I find the answer to my issue I'll be sure to post it here. I'm planning to verify the trigger coil gaps tomorrow ~ I need to find the proper gap setting; I think it's .016 but haven't verified that yet. My issue developed once the engine warmed up in flight, after about 10-12 minutes of flight. It wouldn't do it on the ground and pre-flight ignition test, maybe because I couldn't get it under full load. The brakes on my Zodiac 601HDS aren't that strong/great to hold the ship above 3000-3500rpm.

  • Re: Ignition Circuit -B- Problems

    by » 7 years ago

    @ Roger
    Unfortunately, until now, nobody replied. But I´m still alive :)

    @ Tom (companion in misfortune)
    No solution until now. I will reply in detail tomorrow.
    Today I ´m too tired :)

  • Re: Ignition Circuit -B- Problems

    by » 7 years ago

    Roger ~ you're my hero!! Thanks for the advice to check the trigger coil gaps! That appears to have been the issue with my engine misfire. I found one coil at about a .022 gap and another .018-.020 on the same ignition side. After adjusting them I took a test flight ~ the rpm drop is nearly negligible now; actually the other ignition has more drop than the one that had been acting funky. Overall the engine is running smooth now at all power settings.
    Best wishes and thanks a million for the advice and help!

    p.s. I don't know how to include Gerhard in this post but hope he reads this post and it helps him with his issue too.

You do not have permissions to reply to this topic.