All About ATV Carburetor Jetting
August 1, 2017
The carburetor in your ATV is responsible for mixing air and fuel, and this mixture is fed into the engine. When the mixture of fuel to air is in the correct ratio, your ATV engine will run optimally. However, this ratio can be affected by several influences; and to correct the ratio, you have to re-jet your carburetor. Jetting the carburetor will not only improve performance but also increase the life of your engine. Jetting is required to compensate for changes in temperature, altitude, fuel density and several other internal influences.
Usually, the carburetor jetting is set for a range from sea level to a couple thousand feet. When you are riding at higher altitudes in the mountains, the air is less dense so the carburetor will receive less air. Because of this, the carburetor needs less fuel to maintain the correct air to fuel ratio. Generally, you would go down one jet size for every 2,000 feet elevation. Hence, if your main jet is 160 at sea level, then you need to lower it to 140 to ride at 4,000 feet above sea level.
Lower temperatures alternately create denser air. If you have a small elevation change with a significant drop in temperature, the air will get denser as it gets colder, so you will need bigger jets. Going back to the example, if you have adjusted the jet to 140 to account for the elevation, but the temperature has dropped by 50 degrees, you will have to go back to the 160 setting.
Keep in mind that while you were adjusting the jetting to compensate for altitude, you were using gasoline meant for sea level altitude. When you refuel at 4,000 feet, the gasoline you buy might have additive blends to compensate for the altitude.
At higher elevations, the available gasoline you can purchase is often created to be less dense in order to compensate for lesser air density. Hence, a leaner gasoline would require a larger jet, which means increasing the adjustment. If you are riding at vastly different altitudes then it is better to bring along the required fuel for the entire ride.
In all the above examples, we have talked about adjusting the main jet, which is paramount for engine operations of high speeds. However, multiple jets in the carburetor are adjustable. The pilot jets are adjusted for idle mixtures and low-speed operations. The slide controls or the throttle valves are adjusted for one-quarter open, and off idle mixtures.
Certain carburetors may not have different slide controls, and you will have to compensate by adjusting the needle or pilot jets. Needle jets are mainly controlled for low to mid throttle operations. Needle jets are of two types, one is with a single hole in the middle, and the other comes with side holes as well.