Next on the list of factors is pressure. When you increase the surrounding pressure, you can usually dissolve more gases in the liquid. Think about your soda can. It is able to keep the fizz inside, because the contents of the can are under higher pressure.
Assuming a prop, it depends on how you are propped but with a redline of 6000 rpm, most outboards perform best with a cruise in the 4000-4400 rpm range. If you want top fuel economy, get a floscan or such and see what is the most efficient for your engine and prop.
YAMAHA 5C PORTABLE OUTBOARD MOTOR. The portable Yamaha 5C outboard motor has a 103cc powerhead that develops five brake horsepower (bhp) at 5000rpm with a Wide Open Throttle range of 4500 to 5500rpm. The cylinder head and block are integral with an unboltable hatch in the head to clean the cooling water passages. tried a four-stroke 5 on the Bluey and the old transom fasteners let me know pretty damn quick this wasnât the way to go! As of April 2014 the longshaft Yamaha 5C outboard motor had a price of around $1900 with a spare propeller for $120.