This paper describes an adaptive fuzzy throttle control for an all-terrain vehicle (ATV) powered by internal combustion engine. The design objective is to provide smooth throttle movement and zero steady state speed error, and to maintain a selected vehicle speed over varying road slopes for a 2–30 mile/h speed range. Unlike modern production vehicles which have microprocessor-based engine management systems, the ATV's engine is mechanically controlled via a carburettor. A complete mathematical model of the engine is not available, making it very difficult to apply conventional control techniques. Using experience and data collected from extensive experiments conducted on the ATV throttle mechanism, an adaptive fuzzy throttle control algorithm is designed. A candidate Lyapunov function is employed in the adaptive law synthesis to ensure convergence. Experimental results are presented showing the effectiveness of the control algorithm at speeds below 2.74 mile/h (1.2m/s).