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Discussion Starter #1
I recently purchased a used 06 Ninja 250. After a few rides I noticed that it was leaking a little bit of oil. I asked the previous owner if it had ever leaked oil before and they said no. I did some research and found out it should would be coming from the airbox. I drained the hose and continue to do so every so often.

Today I noticed a bigger pool of oil than normal. And it looks like there's a tiny hole in the bottom of the airbox behind the container for the coolant, so now I'm looking into replacing the airbox.

To other 250 riders, is oil accumulating a lot in the airbox normal? Is there any way I can reduce the amount of oil that accumulates?
 

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It's probably coming from the base of the engine caused by blowby. The engine base is vented back to intake. You might want to inspect the routing of the pressure from the base to the intake. Cars typically have a PCV, positive crankcase ventilation check valve in that line and if it isn't working properly can cause excessive blowby to the intake. Another thing that can cause it is too much blowby getting past the piston rings. Riding it hard keeping the rpms up will cause it to a certain extent. Maybe some owners of your same bike model will chime in.
 

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Another thing to check is your oil level. If base is over-filled with oil, there will be more oil and oil mist being pumped out the crankcase breather which is connected directly to your airbox.
 

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Discussion Starter #4
Another thing to check is your oil level. If base is over-filled with oil, there will be more oil and oil mist being pumped out the crankcase breather which is connected directly to your airbox.
I've put it up on it's center stand. Oil seems to still be over filled, so I'm hoping it's this. And by either riding - or doing an oil change - the issue will be resolved.

Thanks
 

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My guess too would be overfilling. I had an '04 1500 Classic that refused to keep anything over 2/3 in the sightglass. You'd think it would be fine but it always blew the oil out to that level. If it's not excessively overfilled, by that I mean it's a little above the full mark, I'd let it self regulate. Then I'd know how much is too much next time.
 
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I have one of those hand held mityvacs that I would use to suck out the excess oil. Available at Harbor Freight. It's also good for sucking out the fluid in the master cylinder before refilling and flushing the brake lines. As well as pulling a vacuum on the brake line at the caliper.
 
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