I have an '06 Sportsman 450. Today while going on a real quick ride I noticed my belt was slipping very badly. It is a new belt and doesn't have more than 500 miles on it. Two days ago when I rode there was no slipping at all. When I took everything off to inspect it I noticed the inside was full of like a oily black soot. Every so often when I clean the air filter it is always full of the same soot. First, what is causing the soot, and second would that be making the belt slip? When I cleaned it all off and put everything back on the belt wasn't slipping. I have never rolled the machine or anything like that either.

 

Fine black soot is normal after some miles. It is from the belt ware. The cleaner you can keep the clutches the less they will slip and save you a lot in replacement parts also.
Use a air compressor to blow it out good and the wipe down clutches with a contact or brake cleaner that doesn't leave an oily film.

Not sure what would cause that in the air filter.

 

If there is oil in the clutch cover I would check to see if engine shaft seal is leaking oil into the clutch cover and mixing with the belt dust. Just an idea.

 

Not certain that the stuff inside the clutch cover is oil. Didn't smell like oil, but the stuff in the airbox certainly does smell like oil/gas.

 

I would double check on the stuff inside your belt cover. Must be a fair amount to cause it to slip. Some(very little) oil is normal in the air box.

 

The stuff in the airbox is probably from the crankcase breather. It's connected to the small tube on the front of the airbox and runs to the top of the engine(assuming it's the same set-up as my 800).

 

Steep inclines or rolling the machine can lead to oil in the air box.

 

I would agree that it is probably the crankcase vent that is causing an oily substance in your airbox. I have seen it on a few that I have worked on. Check to make sure that your crankcase is not overfull

 

Steep inclines will get oil in your air box, no proplem Polaris even has a drian plug for that.

Once water gets in you belt housing it causes a dark grey soot mess everywhere but the slipping should goes away once the water evaporates,because the belt friction will clean off the soot from the inside sheaves where it matters.