Why is my 2007 Kawasaki KX250F leaking oil out the black brether hose and how can I fix it?

I just purchased a 2007 Kawasaki KX250F in pretty good condition. The previous owner said it was serviced regularily. I went out riding for my first time and noticed it was leaking oil out the black brether hose. I changed the oil but it still seems to still leak oil. Does anyone know how I can fix this problem?

Only time i've ever seen oil blowing out the tubes on a 250f is when the cylinder is worn or scored. Allows blow by pressurizing bottom end, which carries the oil out the tube as more air is flowing out of the tube than usual. I used a mildly scored cylinder on my 11 250f in a pinch and it started blowing oil out the breather the first ride with that cylinder. Replaced with new cylinder problem fixed.

I agree with dmm698 but I wouldn't rule out that the crankcase is overfilled.  The recommended spec's are engraved near the kickstart.

This is a very common problem with 07 kx250f , do a search. We have one we run the oil at the bottom of the sight glass, it seems to blow less oil that way. When you change your oil if you put in the full amount they will often blow a lot of oil on start up. The secret is to put in only about 750 cc run it for a minute or so then add another 250 cc this should get it to the bottom of the glass. A lot of people have rebuilt these motors thinking they had a problem only to have it happen again. The vent hose is too close to the clutch which picks up oil and throws it out.

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