There is a crankcase vent hose that runs from the head cover to the airbox to vent oil vapor from the engine. That oil ends up in the bottom of the air box.

There is also a drain hose that runs from the bottom of the air box and hangs down under the center of the motor. It has a little plastic plug in the end of it that you can remove to drain the oil that condenses and collects in the air box. Every time you change the oil it should be opened and drained.

The amount of oil seems excessive.  There is an oil separator inside the head where the breather tube attaches.  #41 in this fiche
http://www.bikebandit.com/oem-parts/2008-suzuki-boulevard-s40-ls650/o/m147543...
It is made up of metal screen material.  If it is missing, that could be the cause.
I don't know if you can poke something in the tube to see if you can feel it is there or not.
If you remove the air box, the breather just vents to the outside, but it needs a breather filter so you don't suck dirt in to the engine.

Do you still have the stock vacuum petcock?  Have you checked your oil level?

If the diaphragm in the petcock is failing, it can allow fuel to flow into the engine intake, and the fuel then seeps down past the piston and dilutes the motor oil and raises the oil level.  If you ride the bike like this, it makes a lot of blow by......and in severe cases the engine will be really down on power as the oil/fuel level is so high the crankshaft is in a pool of oil/fuel.  (This can also happen if you have switched to the Raptor manual petcock and forget to shut it off).

Check you oil level and smell the oil and see if it has a fuel smell.

Also....the stock airbox and filter work well.  Unless you want a pod filter for looks - there is really no reason to switch to a clamp on Pod filter.

You can put a K&N filter in the stock airbox.....they do have to be cleaned and oiled, and it is time consuming and messy.  The paper air filter can be blow out with compressed air, and replaced when it becomes too old.

When I bought the bike and changed the oil, 4 litres came out!!  Put back 2 litres of rotella, did not check the airbox.
The engine is being given the once-over for tensioner, petcock, cables etc., all the good stuff. May keep the stock air filter if K&N isn'treally necessary.  
This forum is a major useful resource, Thanks all!

zipidachimp wrote on 01/17/15 at 12:40:14:


It really isn't necessary; although, I recommend it.  It makes mine more responsive and probably cheaper in the long run.  It is easy to clean as well.

Best regards,

Took off the exhaust today, the airbox is becoming a pain to get off and drain. What am I missing?

Dave wrote on 01/17/15 at 03:54:41:

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