Oily substance dripping from air box...what the ???

[JasonRan]

So I rode my KDX 200 this weekend about 40 miles in some relatively dusty conditions. When I got home and parked it in the garage, I noticed that it was leaking an oily substance from the rubber "nipple" on the bottom of the air box. I took the seat off and noticed that almost the entire inner part of the air box is covered in the same oily substance. It does not appear to be the oil that is used to oil the filter though. There was also considerable dirt and dust in there. It does not appear to be blowback from the carb, because the inside of the air filter is perfectly clean, and the intake on the carb is spotless. This may be perfectly normal, but I have never noticed it before. I was running some very high RPM's and WOT during my ride, which I normally don't do. Also, I do not have the air box lid on. Just wondering if anyone had experienced this or can tell me if it's normal. Thanks!

 

[NM_KDX200]

I had this same problem under the same conditions- WOT and hard riding-, twice, and tracked it down to the vent hose from the crankcase. That hose vents into the air box and I was running a) ATF in the gearbox and b) a full quart of it. I think the oil just got hot and thin and blew out the tube into the box. I've gone back to 10-30w and just under a quart and haven't had the problem again.

 

[JasonRan]

Very interesting...I never thought about that. I rarely ride as hard as I did this past weekend. I'll check out my vent tube...we may have solved the mystery. Thanks!