cases, detonation causes engine overheating, rough- ness, or loss of power. Detonation is characterized by high cylinder head  temperatures, and is most likely to occur when operat- ing 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  flight operations: fuel must be available to the engine under all condi- tions of engine power, altitude, attitude, and during all  approved flight maneuvers. [Figure 4-12] Powered parachutes have fuel pump systems. The  main pump system is engine-driven and sometimes an  electrically-driven 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 electrically-driven auxiliary pump is controlled  by a switch in the cockpit. Figure 4-12. Fuel pump system.  • 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  your POH you should drain old fuel out and  replenish with fresh fuel. • Operating the engine at high power settings  with an excessively lean mixture. • Detonation also can be caused by 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 Pumps Fuel Plunger Primer Fuel Systems 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 insula- tor, or other damage in the cylinder that causes a part  to heat sufficiently to ignite the fuel-air charge. Preig - nition causes the engine to lose power, and produces  high operating temperature. As with detonation, pre- ignition may also cause severe engine damage, be- cause the expanding gases exert excessive pressure on  the piston while still on its compression stroke. 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. Detonation and preignition often occur simultaneous- ly and one may cause the other. Since either condition  causes high engine temperature accompanied by a  decrease in engine performance, it is often difficult to  distinguish between the two. Using the recommended  grade of fuel and operating the engine within its prop- er temperature and RPM ranges reduce the chance of  detonation or preignition. The fuel plunger primer is used to draw fuel from the  tanks to supply it directly into the cylinders prior to  starting the engine. This is particularly helpful during  cold weather when engines are hard to start because  there is not enough heat available to vaporize the fuel  in the carburetor. For some powered parachutes, it is  the only way to deliver fuel to the engine when first  starting. After the engine starts and is running, the  fuel pump pushes fuel to the carburetors and begins  The fuel system is designed to provide an uninterrupt- ed flow of clean fuel from the fuel tank to the engine.  See Chapter 3 for more information on fuel tanks. The  4-10