Oil In Air Box
 

I recently bought a used KLX250sf and as one of my things to check was the air filter. Once opened the air box had UNI air filter installed and a bunch of bugs. So I decided to clean around and then i noticed the lower part of the filter was soaked in oil? As much as i tried to dry it off it was still oily,why did this happen? should I change it or just wash the filter?

Remove filter, wash, re-oil, reinstall, good to go.

I recently purchased a KLX250S and noticed the same thing when I inspected my air filter. Although I didn't have oil pooling at the bottom of the air box.

Initially I thought it was because I put too much oil in during a recent oil change and it worked it's way up to the air filter. But then I learned the filter is suppose to be oily. I'm not sure how oily though. It seemed like the rim of my filter was pretty oily so I squeezed the excessive oil into a rag.

I just ordered a K&N filter so it will be a moot point for me soon.

Not a problem, the filter is supposed to be oiled. If you put too much on it will just drain out of the drain tube.

If you do a lot of highway riding, oil can actually come up the crankcase vent as well.

On my longer highway trips with a lot of sustained 70 mph riding, often I will find a little bit of oil at the bottom of the air box.

They all do it, nothing is wrong.

I think most of the oil observed in this scenario is from the filter itself. However, depending on crankcase pressure, it's also not that unusual to have a small amount of oil aspirated into the airbox tube. So unless you're bleeding a really noticeable amount of oil into the airbox, I wouldn't worry about it too much.

My KLX likes to puke a bit of oil back into the airbox if I fill the oil more than dead even between the hash marks on the oil sight glass FWIW.

Even a K and N filter requires oil on it to work properly.

Very true, linkin, but if you have oil dripping out of a K&N after servicing, you probably know you have waaaaay too much oil on it. On these foam filters, even with the super tacky specialized filter oil, if you get just a little rich with the oil, gravity will usually let a little of that oil soak to the bottom of the filter and on to the airbox. If you're using motor oil or a thinner oil, you're just about guaranteed some oil to come out of the airbox. Even that thick, tacky oil can seep a little when you get full engine for awhile.

Still, it's not too unusual to get a little oil from the crankcase into the airbox tube. It should only be a little bit, however.

Oil in Airbox klx250s
 

I just bought one and brought it home on my trailer laying on it's side. When I checked the air filter I noticed it was soaked in oil and the there was oil built up in the box itself. I've read about the oil blowing back into the airbox and also someone mentioned this could happen if the bike was on its side.