I have a Yamaha yfz450. It has aftermarket shocks, steering control thing, tires, foot bars, revbox, recluse clutch kit, yokosomething pipe, kn air filter, coolant heatsink, and a after market **oil tank**

When i first got it none of this was on here and it never leaked oil.
Then recently after i got all this done, it started leaking oil out the back near the swing arm.

I checked the air box and it was full of oil.

I checked the oil level and its fine but still cant solve this problem.

Can somebody help me figure out why the oil is filling the air intake box?

 

If you removed that "little black box " on the left rear frame put it back on- that is a oil /vapor separator- the oil flows back down to the starter clutch housing and the vapor goes into the air box- never pipe that drain line directly to your air box