Reading spark plugs?
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  1. #1
    Junior Member Tin7117's Avatar
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    Reading spark plugs?

    I just changed out new spark plugs for my cm400t and wasn't too sure how to read the old ones to indicate my engine's condition. Any help to why the threads have oil on them?Reading spark plugs?-20191018_175111.jpgReading spark plugs?-20191018_175046.jpg

  2. #2
    Senior Member Rscottp's Avatar
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    They both look acceptable to me but they should match better IMO. Are the carbs synched?
    1981 Honda CX500D
    1974 Honda CB450
    1986 Yamaha Radian 600

    Martha's Vineyard Ma

  3. #3
    Super Moderator longdistancerider's Avatar
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    The one with the more white ceramic is close to right, should be more so. The other is a little more rich.
    The oil on the threads is due to the plugs not being tight enough. Note the difference in the crush/seal washers. The plug with oil all the way up also shows it creeping past the washer plus it's thicker than the other one. The plugs actually have a torque spec of 11-14 ft.lbs.
    Jim O'Brien
    1979 CM400T "road bike" modified for travelling
    1978 CB400T1 restored
    1972 CL350 nuts and bolts restore in progress


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  5. #4
    Junior Member Tin7117's Avatar
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    ah, thank you both for the info. I'm not sure if the carbs are synched.

  6. #5
    Senior Member f100owner's Avatar
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    Plugs looked a lot like mine after about 300 miles on a top-end refresh.
    CL350K0
    2016 Harley Ultra Limited
    1971 Ford F100 Flareside (project)
    2016 Ford Expedition
    2018 Ford F150

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