corrected, can quickly lead to failure of the piston, cylinder,  or valves. In less severe cases, detonation causes engine  overheating, roughness, or loss of power. injection systems. The fuel must be available to the engine  under all conditions of engine power, altitude, attitude, and  during all approved fl ight maneuvers.  [Figure 4-17] Detonation is characterized by high cylinder head temperatures  and is most likely to occur when operating at high power  settings. Some common operational causes of detonation  include: Detonation may be avoided by following these basic  guidelines during the various phases of ground and fl ight  operations: Preignition occurs when the fuel/air mixture ignites prior  to the engine’s normal ignition event. Premature burning  is usually caused by a residual hot spot in the combustion  chamber, often created by a small carbon deposit on a spark  plug, a cracked spark plug insulator, or other damage in the  cylinder that causes a part to heat sufficiently to ignite the  fuel/air charge. Preignition causes the engine to lose power  and produces high operating temperature. As with detonation,  preignition may also cause severe engine damage because  the expanding gases exert excessive pressure on the piston  while still on its compression stroke. Detonation and preignition often occur simultaneously and  one may cause the other. Since either condition causes high  engine temperature accompanied by a decrease in engine  performance, it is often diffi cult to distinguish between the  two. Using the recommended grade of fuel and operating the  engine within its proper temperature and RPM ranges reduce  the chance of detonation or preignition. The fuel system is designed to provide an uninterrupted fl ow  of clean fuel from the fuel tank to the engine. See Chapter  3, Components and Systems, for more information on fuel  tanks. See earlier section in this chapter for specifics on fuel  Sometimes an electric auxiliary pump is provided for use in  engine starting and in the event the engine pump fails. The  auxiliary pump, also known as a boost pump, provides added  reliability to the fuel system. The electric auxiliary pump is  controlled by a switch in the fl ight deck.  WSC aircraft with carburetors have engine-driven fuel pump  systems. A diaphragm pump is the primary pump in the fuel  system for two-stroke engines. Air pulses in the crankcase  actuate a diaphragm and provide fuel under pressure to the  carburetor. Four-stroke engines have a mechanical pump  driven directly off the engine. • Using a lower fuel grade than that specified by the  aircraft manufacturer or operating the engine after  it has been sitting for an extended period; after 3  weeks or as indicated by the POH, drain old fuel and  replenish with fresh fuel. • Operating the engine at high power settings with an  excessively lean mixture. • Extended ground operations. • Make sure the proper grade of fuel is being used. Drain  and refuel if the fuel is old. • Develop a habit of monitoring the engine instruments  to verify proper operation according to procedures  established by the manufacturer. Fuel Systems Fuel Pumps  Fuel tank$^{PRIMER}$ Fuel pickup with screen Carburetor fuel bowl Optional primer plunger Fuel filter Optional primer bulb used to pump fuel into the carburetor fuel bowls for starting (an alternative electric fuel pump can also be used) Fuel fill with  integral vent Throttle Control Engine driven  fuel pump Figure 4-17. Typical Carburetor Fuel System. 4-13