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Spark plug 1-3 color difference - Aeroprakt Panama

in General Tech Discussion 9 years ago
I am doing the 250 hr maintenance down here in Panama on a Rotax 912 ULS for an Aeroprakt 22L2. Iridium spark plugs are only 75 hrs. Number 2-4 on left side are ok. Number 1-3 on right side are very different. # 1 (on front next to propeller) is black velvet and number 3 (next to carb) is white. Any one could tell me why would one side only show such difference between the two cylinders? Photo attached.
Thanks
sparkplug1-3.jpg (You do not have access to download this file.)

  • Re: Spark plug 1-3 color difference - Aeroprakt Panama

    by » 9 years ago

    Ricardo,

    It looks like the fuel is not atomising properly and the 'heavy' fuel droplets are going straight to the front cylinder. Check all carb drillings are clear including the small ones near the inlet of the venturi. Clean them through using a can of carb cleaner.

    I am assuming that you have checked obvious other causes like air leaks, etc.

    Kevin
      
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  • Re: Spark plug 1-3 color difference - Aeroprakt Panama

    by » 9 years ago

    This is a normal occurrence if you have been at idle speed. Kevin is correct; the #1 intake manifold is the longest and at idle the mixture distribution is not optimal. the manifold is designed to be optimal at 5000-5800 RPM.
      
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  • Re: Spark plug 1-3 color difference - Aeroprakt Panama

    by » 9 years ago

    Do both the plugs on #1 cyl. look the same? An answer would depend on whether it is only one plug or both on #1.

    This could be just prolonged idle running, but that plug looks pretty black and a thicker coat of black and not just a thin dusting of dry black velvet.

    One way to tell is if you put that plug back in a ran the engine up around 4000 rpm for approximately 4 minutes or so and then pull throttle back to idle and shut the engine down as soon as you pull it back then there shouldn't be any dry black velvet look to that plug. It should then be burned off.

    If it's only one plug it could be just a bad plug, a bad plug wire or long idling. Change the plugs and go fly and look again, remove the rubber plug boot off the plug wire and trim the wire back about 3/8" and screw the plug boot back on. If it is both plugs also do a compression leak down test. After you check these you could move on to other checks, but always start with the simple things first and rule them out.



    p.s.
    I don't see any thermal conducting paste on the plug threads?

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

      
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  • Re: Spark plug 1-3 color difference - Aeroprakt Panama

    by » 9 years ago

    Good morning everyone:
    Thanks for all the advise.
    Yes, both plugs on front are black and both on back are white. We did check the compression and it was within limits. Funny thing is that the other side -carb- is not showing this difference, and plugs all look normal.
    I will check the carb drillings. I ran the engine yesterday until temp was up to 50°C, turned it off for 5 minutes but had to crank it 4-5 times before it ran. Normally it runs on the first crank. After that it was ok, took it up for a 30 min ride. Magnet test at 4000 rpm was ok.

    I also wondered if it could be an electrical problem on that side.

    Roger, what do you mean by thermal conducting paste?

    Thanks
    Ricardo
      
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  • Re: Spark plug 1-3 color difference - Aeroprakt Panama

    by » 9 years ago

    Ricardo,
    You do not have an electrical problem. It is normal to have #1 plugs darker.
    Rob
      
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