Outboard marine engines work much hard than automobile engines. They do not have a feature that allows them to coast after a surge of power and momentum, like cars or trucks. For this reason, outboard engines wear out faster, absorb more heat over a longer period and work under a constant load. Outboard engine cylinders also take a beating when it comes to ingesting water from their environment or cracking as a result of improper winterizing procedure. Some outboard cylinders simply crack from heat and stress.
Observe the starting sequence of your engine on your next outing. Upon starting the engine, note whether the engine lugs during starting, or seems to pound or hesitate before the engine starts. Stop the engine. Unclasp the top engine cowl case.