[THEFERMANATOR]

Outboards run on the water, and you tend to not get alot of dust and debris when out on the water so air filters aren't a big neccesity. As for running without the airbox, the carbs ar jetted for the restriction from the factory. If you add air, you have to jet up about 6 sizes for an OMC to compensate for the airbox removal(but 6 sizes is the MINUMUM and you have to be careful at that to check it). The OEM's use the airbox as a restrictor to help smooth out the mid range transition some and to keep them from leaning out in the mid range. This helps the driveability of the engine, but means you have to jet down some on the top end to keep it at a good fuel air ratio. The old 200XP from 86-87 didn't have a restrictor in the airbox, but they had 74 jets whereas the 225 with the restrictor would have 65's or close to that in them. The 200XP's ran AWESOME on the top end with there MASSIVE carbs and open airbox, but they were known for burning up if ran in the mid range for extended periods and many were converted over under warranty to the 225 set-up due to it.

And I haven't seen many I/O's with air filters on them. ALL of them do have flame arrestors, but this is for USCG requirements. They look like air cleaners, but they flow alot of air and are only there to prevent flames from the intake catchong any vapors on fire in the bilge in case of a back-fire. Some do use a K&N filter for qa spark arrestor, but it is mostly for the USCG regs and not for filtering.