Re: Generally, does swaping the carb setup of ex. 200hp to a 150hp make the increase?
On an auto engine, switching from a 2 barrel to a 4 barrel will decrease the restriction so there is a gain in horsepower. However, most auto enthusiasts will also Change a cam and use headers along with the bigger carb.
Outboards however are set to a specific horsepower by (2 cycle) port timing and compression, given a series of engines with the same bore and stroke. Thus, on a 2 cycle outboard engine, a bigger venturi carb will result in very minor increases in power due to decreased airflow restriction and on bigger engines you MIGHT notice maybe 1 MPH more top end. However, frequently the carbs are the same size venturi in the higher horsepower engine but jetted differently to account for the higher airflow the higher horsepower engine has (due to a generally higher operating RPM and more aggressive porting). Thus, there is no decreased restriction when you use carbs off a higher horsepower engine and no gain.
4 cycle engines are set to horsepower by cam timing and valve size and again, a carb change will only result in minor gains.
Most outboards are designed to be at the top of their output for a given horsepower and without major modifications, there are no bolt-on horsepower increases.
