What Is The Difference Between A Salt Water Outboard Motor And A Fresh Water Motor?

Growing up next to the ocean, I have operated my boat in both fresh and salt water.  In fact, up until a few years back, there really was no differentiation between fresh or salt designated models offered by the major manufacturers.  If you look closely at what differentiates a "salt water" model from a "fresh water", you will see it is a matter of a few external parts that are more corrosion proof or where stailess steel replaces painted.  

What I have done is hose down the engine after ever use in the salt water and have run fresh water through the colling system.  There is no reason why your engine should not continue to perform just as it has in fresh water.  And even if you are not able to do so after each use, it is very unlikely any harm would be done.

The only difference that I have found is that the "salt water" engines have a few external parts that are meant to resist corrosion more than the fresh water.  I am guessing that has to do with the salt.  Yet, washing and running fresh water through my engine has not caused me any problems.  In fact, my engine is over 20 years old right now, and other than normal maintenance, no issues.

There are 2 stroke outboard motors and 4 stroke outboard motors.
Many fresh water lakes have outlawed 2 stroke outboards.
Two stroke motors, require the mix of 2 stroke oil within the gas.  This system tends to expel oil with the exhaust there fore fowling the water, whereas, a 4 stroke operates more like an automobile.
One can operate a 2 or 4 stroke outboard motor in either fresh or salt water environment.  Fresh water being less corrosive to the equipment.