What year is this mercury outboard 40hp serial 2877503 need a prop?

To determine the year of a Mercury 40hp outboard motor with the serial number 2877503, you can refer to Mercury's serial number lookup charts, which typically indicate that this serial number corresponds to a model from the mid-1980s. Specifically, it is likely from around 1986. For the correct propeller size and pitch, you should consider the specific application and boat specifications, as well as consulting a marine professional for recommendations.