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87 90ETLH leaking oil into carbs/breather box

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  • 87 90ETLH leaking oil into carbs/breather box

    Slow oil leak into/thru the carbs into the breather box, creating a puddle in the bottom of the box. Eventually leaks into bottom cowling. Worse problem when motor is tilted up. I've seen others online with similar issue, some say it's a check valve (or lack thereof) problem. What's the best way to fix this?

  • #2
    test/ replace the check valves


    • #3
      My 1999 C90 always has oil puddled up in the air box...guess when the gas in there evaporates it leaves behind the problem here at all....


      • #4
        I understand there's 2 oil pumps: one that has a check valve in the pump and one that has them inline. Assuming the fix is replacement of entire pump for one and replacement of individual check valves for the other? If I have oil lingering in all three carbs, would that indicate I have the oil pump with one check valve?


        • #5
          the early kien pump had the checkvalves in the pump.
          the later replacement and 1990 up mikuni pumps used inline check valves.