What is the purpose of a primer pump in an outboard motor?

The purpose of a primer pump in an outboard motor is to inject fuel into the cylinder before starting. When an engine is cold, it often requires an enriched fuel mixture to facilitate easier starting. The primer pump is designed to manually push fuel from the fuel tank to the engine's intake system, ensuring that there is sufficient fuel available when the engine is cranked. This helps to create a vapor-rich mixture that is more conducive for combustion, especially in cold conditions where fuel may not vaporize as effectively.

By priming the engine in this way, the likelihood of a successful start is significantly increased, ultimately allowing the motor to start and run smoothly from the outset. This function is especially important for outboard motors, which may not naturally draw fuel effectively without assistance from the primer when the engine has been sitting idle for a period of time.