Air Filter

Early (2011–2012) Filter System 

OSSA used two different styles of air filters.  Early bikes came fitted with a filter assembly (part number 9310010211) that had to be completely detached from the throttle body for cleaning.  This is item #1 in the early parts diagram shown below.  Item #13 is the intake air temperature sensor, and its mounting is quite unusual.  There are two rubber “whiskers” that hold this sensor in place.  You must stretch the whiskers through holes in the sensor to remove or install it.  This is a recipe for eventual failure.   

I can't recommend using the TwinAir filter for early bikes because it lacks any mounting system for the intake air temperature sensor.

Late (2013–2015) Filter System

The foam filter itself (part number 9350010213) was easily replaced and is still available in the aftermarket.  Unfortunately, there is no simple upgrade path to this system for early bikes. 

Although the later filter system is arguably better, item #3 in the late parts diagram (air filter housing assembly) became unavailable shortly after OSSA's demise.  It is part number 9330010213.  If you find one, buy it! 

I suspect if the rubber whiskers ever break, you could cannibalize a filter assembly for the early bikes to cobble together something workable.

Filtered Airbox Top

Years ago, I bought some Jitsie filtered airbox tops (part number JI712-999).  This is helpful with the early bikes as you can clean the filtered top instead of the internal airbox filter.  However, it does affect the fueling, and the fit is far from perfect.