Hello maybe someone can give me some advise in this matter. I Have a Rotax 912.  the problem I am having is that the engine starting running rough, so we went through and worked on the carbs and replaced one of the carb clamps. we got everything setup and still had the same problem. We pulled the spark plugs and all looked good until I got to the plugs on #3. Both top and bottom were wet and looked as thought they were not firing. we cleaned all the plugs and checked the gap. (.025). next we cleaned the carbs, and reset everything. I cut a quarter in off the plug wire and replaced the head. We fired it up and got the same result. High trust at first gives good steady run then it starts to run rough.  Runs real rough at idle.  Checked the plugs again and same thing all look good except plugs on number 3. Both wet and not firing. The confusing part is this top on one mag and bottom on other mag. How can I get both not firing on one cylinder but the other 3 are fine top and bottom. Obviously there is something I am missing. Has anyone else ran into this and any advise.

  • Re: No spark on #3

    by » 5 weeks ago


    It seems that it is cable related issue.


    Thank you said by: Larry E Morton Jr

  • Re: No spark on #3

    by » 5 weeks ago


    Did you weigh the floats? Also do a carb sync rough idle may cause flooding.

    As per Maintenance Manual Line (MML) let the floats dry for 1-2 minutes. Only weigh dry floats. Due to their higher compaction rate, the dry weight of the new floats (pair) part no. 861188 may be higher than the previous floats. But in no case the max. weight (of both floats together) is allowed to exceed 7 grams and so still applies. See relevant Maintenance Manual Line Chapter 12-20-00.


    Thank you said by: Larry E Morton Jr

  • Re: No spark on #3

    by » 5 weeks ago


    The plugs on Cyl#3 fire at the same time as the Plugs on Cyl#4 in a Wasted Spark Ignition.

    The Top And Botton Plugs are on completely different ignition circuits (Mags).

    So either both Plugs on #4 are also dead or the plugs in #3 are firing and just not lighting the fuel charge and something else is the problem.

    It Isn't a Plug Problem!!!

     

    I would look at the #1-3 Carb.  Is sound like it is flooding,

    Check the Floats and The Float valve.

    If the #1-3 Carb is excessively rich, the #3 Cyl will intercept the bulk of any un-vaporized, liquid fuel before it can make it to cyl #1.


    Bill Hertzel
    Rotax 912is
    North Ridgeville, OH, USA
    whertzel1@yahoo.com
    Clicking the "Thank You" is appreciated by all.

    Thank you said by: Larry E Morton Jr

  • Re: No spark on #3

    by » 5 weeks ago


    one finding can check the EGT  level? on rich side the EGT may be LOWER than Other.The lowest side carburetor can me checked for rich cause, float fault etc?

     


  • Re: No spark on #3

    by » 5 weeks ago


    Check that the choke ( enrichment) lever is closed and against the stop. i just went through this..


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