How an Outboard Choke Works

By Matt Scheer

An outboard motor is a propulsion and navigation machine for a boat. The outboard motor features an adjustable choke that changes the amount of fuel in the fuel and air mixture.

Function

Outboard motors feature a choke when they work by internal combustion. When the choke is activated, the amount of air entering the carburetor is reduced, increasing the amount of fuel that enters. This change in ratio between fuel and air helps the engine first start up.

Significance

Without a choke, an outboard internal-combustion motor may not start up when cold. This is because gasoline does not vaporize efficiently when cold. By increasing the amount of fuel in the combustion chamber, the choke helps the engine start.

Mechanism

When the operator activates the choke through a pull handle, button, or knob, the choke solenoid, a coil, expands, restricting the area through which air enters the carburetor. This restriction in space lowers the amount of air coming into the carburetor. At the same time, the pressure in the carburetor lowers, pulling in more fuel to the combustion chamber.