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I just performed an 25 hr oil & oil filter replacement and replaced the spark plugs which had 100 hrs on them. The carb floats were replaced at the previous annual and weighed correctly during this years annual. When inspecting the plugs, the number one cylinder plugs were noticeably darker than any of the other plugs which were uniform in color. This would suggest the cylinder is running rich. How is this possible (#1 is furthest from the carburetor)? Do I need to be concerned? What needs to be adjusted? There are 400 hrs on the engine which generally runs fine. 90% of the time using 100 LL Av gas w/ Decalin additive.

8413_1_C419D258-895D-493C-B32E-11FA75C2FEB3.jpeg (You do not have access to download this file.)
  • Re: Cyl. No. 1 Rich

    by » 4 years ago


    Hi Rob,

    that's nothing to worry about, really. Looking closely I suggest you check the gapping. Done.


  • Re: Cyl. No. 1 Rich

    by » 4 years ago


    Peter~
    i appreciate the feedback, thank you. The noticeable difference in the plug color and limited to a single cylinder piqued my interest. I was not sure if the delta in color could be predicting a valve adjustment for cyl. #1. It seems counter intuitive one cylinder could be running so significantly rich.

    Again, thank you sir.


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