How Does an ATV Carburetor Work?

All-terrain vehicles, also known as ATVs, operate with internal combustion engines. Internal combustion engines are powered by a reaction caused by the burning of a combination of fuel and air. A carefully measured mixture of air and fuel is trapped in a combustion chamber called a cylinder. The cylinder, connected in a line with several other cylinders to form what is called an engine block, has a piston at one end. The trapped mixture of air and fuel is ignited using a spark plug, and the resulting explosion pushes the piston out of the cylinder. The movement of the piston produces energy for the engine. The mix of fuel and air that is ignited in the cylinder must be in the correct proportions or the engine will not fire properly. The device that regulates the flow of both air and fuel into the cylinders is called a carburetor.

The movement of the piston down into the cylinder draws air through the carburetor, which causes the pressure in the carburetor to drop. The lowered pressure draws the fuel up into the carburetor, into a container with a float. The float shuts the intake valve when the container gets too full, and reopens it when the level of fluid drops. As the ATV throttle is pressed, fuel is drawn through a jet and mixed with air on its way into the cylinder.

There are three different jets used for controlling the amount of fuel sent into the cylinders by the carburetor of an ATV. The pilot jet is used to provide fuel to the engine when the ATV is set to idle and up to one-eighth of the throttle capacity. This jet has a small calibrated hole, allowing only a very small amount of fuel to flow through. The needle jet is a slightly larger hole, providing fuel when the throttle is set to a level between one-eighth and three-fourths of the throttle capacity. The main jet has the largest opening, providing the most fuel to the engine. This jet is in use when the throttle is at three-fourths capacity or more.