Apr 17, 2007
I was just wondering if there is something wrong with my bike or not. My bike is a 1999 yz 125. I happened to look at the top of my skidplate and noticed that some black oily stuff had collected there. I got to looking and noticed it had come out of a tube. I followed the tube to see where it came from. It comes from the cylinder just above where the pipe hooks to the cylinder. I looked at the parts fiche on yamaha and it showed that this is where the valves are. I also noticed that when I start my bike exhaust comes out of this tube. You can feel it blowing out pretty hard. Im just wondering if this is normal or not. First two stroke ive ever owned. Always ran four strokes. Any advice would be appreciated.


Oct 19, 2006
That's normal. The exhaust valves don't seal perfectly exhaust side of the cylinder. This is half intentional. Exhaust gas (full of oil) blows by the valve and keeps it lubed and clean. That hose is just a vent, it directs any blow-by down towards the ground so it doesn't get all over your bike.
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