Other factors that affect jetting are rev limiters, altitude and fouled plugs if your jetting is off. Increased engine performance usually means an increased demand for fuel so learning ATV carburetor adjustment techniques is important. #2 – The second thing you need to know is that aftermarket performance parts will change your jetting requirements.

Lastly your main jet controls the flow of fuel between the three quarter and wide open throttle positions. The needle jet controls the flow of fuel from the one eight position up to about the three quarter throttle position. The pilot jet, or pilot screw as it is sometimes referred to, controls the flow of fuel between Idle speed and about one eight of wide open throttle (WOT). Each jet is effective for a specific throttle position range. #1 – The first thing you need to remember is that ATV jetting refers to throttle position, not engine rpm. A comprehensive installation guide will come with the jetting kit you purchase for your make and model of ATV so instead this guide will focus on explaining the basic principles of how ATV jets work. Removing the carburetor is likely the best approach.You can tune your own ATV jets and avoid common jetting mistakes if you understand some jetting basics, explained below. Old gas blocking up the pilot jet is a common problem, and the only fix is to remove the jet and clean it. Any blockage here, and you’ll have difficulty idling. Your Pilot Jet is responsible for supplying the gas at idle. Now reduce the idle screw (not air-fuel mix screw) to where the engine idle is smooth, anywhere from 1000- 1500 rpm.Within that window of both stalls, set the screw where the revs are at their highest.Restart, idle the engine and turn the screw (clockwise this time) until it stumbles and stalls.Keep turning until it stumbles and stalls.Start the engine and have a helper balance the throttle while you turn the mix screw anti-clockwise until the engine runs by itself.Return the screw to its original setting.Turn the engine off, find your base setting by turning the pilot screw (mix screw) all the way home (clockwise) until it seats, counting the number of turns (about two is normal).

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