Outboard motors have four main types of enrichment systems to help with cold starting. These are traditional manual chokes, chokes controlled by an electric solenoid (usually activated by pressing the key in when cranking), valves that allow extra fuel into the mixture until the valve warms up and shuts off the extra fuel, and EFI controlled by the ECU using the engine's current recorded temperature as an input.

The Yamaha prime start enrichment system

The Johnson and Evinrude primer solenoid

Johnson and Evinrude outboards use a specific type of primer solenoid that is both electrically activated and has a small red lever for manually overriding

The choke on a carburettor

The choke is the simplest way for an outboard to cause more fuel to be added to the mixture before being drawn into the engine.