engine due to fuel evaporation in hot weather, to supply sufficient fuel to maintain stoichiometric combustion under heavy load with wide-open throttle, or a combination of the two. Fuel demand is low at idle and there is more than enough manifold vacuum to draw sufficient fuel for combustion, even if the fuel pump is switched off. Gasoline engines that are much smaller than the typical automotive engine are usually carbureted for economic and engineering reasons. Dieseling can occur in such engines. These engines include those installed in small generators, mopeds, scooters, small motorcycles, all-terrain vehicles, and most lawn and garden power tools. Potential causes Dieseling can occur for several reasons: Built-up carbon in the ignition chamber can glow red after the engine is off, providing a mechanism for igniting unburnt fuel. Such a thing can happen when the engine runs very rich, depositing unspent fuel and particles on the pistons and valves. Similarly, rough metal regions within the piston chamber can cause this same problem, since they can glow red. It has also been suggested that an improperly rated spark plug can retain heat and cause the same problem. A carburetor that does not completely close can contribute to running once the engine is off, since the extra fuel and oxygen mixture can combust easily in the warm piston chamber. Similarly, hot vaporized oil gases from the engine crankcase can provide ample fuel for dieseling. Incorrect timing. An engine that runs too hot or too lean may produce an environment conducive to allowing unspent fuel to burn. An idle speed that is too fast can leave the engine with too much angular momentum upon shutdown, raising the chances that the engine can turn over and burn more fuel and lock itself into a cycle of continuous running. Another potential "run on" problem after an ignition has been turned off can be attributed to one or more inlet valves that are not sealing fully allowing the piston motion to pull a fuel mixture in when technically the valve is shut. In Air Rifles The term is also used to refer to the deliberate or accidental burning of oils or similar flammable hydrocarbons when an air rifle is discharged. A spring or ram-powered air rifle works by a piston rapidly compressing the air in the chamber behind the projectile forcing the projectile (usually a pellet) out at speed. Where the air contains