Probable Cause Isolation Procedure Correction Engine fails to start 1 Engine runs rough 2 Low power 3 Engine idles improperly 4 a Induction system obstructed b Air leaks a Loose air ducts b Leaking intake pipes c Engine valves sticking a Restricted intake duct b Broken door in carburetor air valve c Dirty air filter a Shrunken intake packing b Hole in intake pipe c Loose carburetor mounting d Bent or worn valve push rods Inspect air scoop and air ducts Inspect carburetor mounting and intake pipes Inspect air ducts Inspect intake pipe packing nuts Remove rocker arm cover and check valve action Examine intake duct Inspect air valve Inspect air filter Inspect packing for proper fit Inspect intake pipe Inspect mount bolts Inspect push rods Remove obstructions Tighten carburetor and repair or replace intake pipe Tighten air ducts Tighten nuts Lubricate and free sticking valves Remove restrictions Replace air valve Clear air filter Replace packing Replace defective intake pipes Tighten mount bolts Replace worn or damaged push rods Figure 3-8.  Common problems for troubleshooting induction systems.  system is not a ground boost system and it is not used to ever  boost the manifold pressure above 30 inches of mercury. A  true supercharged engine, called ground boosted engines, can  boost the manifold pressure above 30 inches of mercury. In  other words, a true supercharger boosts the manifold pressure  above ambient pressure.  enough to ensure complete fuel vaporization and, thus, even  distribution. At the same time, it must not be so hot that  it reduces volumetric efficiency or causes detonation. All  reciprocating engines must guard against intake air that is too  hot. As with any type of supercharging (compressing intake  air), the air gains heat as it is compressed. Sometimes this  air requires cooling before it is routed to the engine’s intake  ports. With these requirements, most induction systems that  use internally driven superchargers must include pressure and  temperature-sensing devices and the necessary units required  to warm or cool the air. Since many engines installed in light aircraft do not use  any type of compressor or supercharging device, induction  systems for reciprocating engines can be broadly classified  as supercharged or nonsupercharged.  [Figure 3-9] Supercharging systems used in reciprocating engine induction  systems are normally classified as either internally driven or  externally driven (turbosupercharged). Internally driven  superchargers compress the fuel/air mixture after it leaves  the carburetor, while externally driven superchargers  (turbochargers) compress the air before it is mixed with the  metered fuel from the carburetor.  The simple internally driven supercharger induction system  is used to explain the location of units and the path of the  air and fuel/air mixture. [ Figure 3-10]  Air enters the system  through the ram air intake. The intake opening is located so  that the air is forced into the induction system, giving a ram  effect caused by the aircraft moving through the air. The air  passes through ducts to the carburetor. The carburetor meters  the fuel in proportion to the air and mixes the air with the  correct amount of fuel. The carburetor can be controlled from  the cockpit to regulate the flow of air. In this way, the power  output of the engine can be controlled. The manifold pressure  gauge measures the pressure of the fuel/air mixture before  it enters the cylinders. It is an indication of the performance  that can be expected of the engine. The carburetor air  temperature indicator measures either the temperature of the  inlet air or of the fuel/air mixture. Either the air inlet or the  mixture temperature indicator serves as a guide so that the  temperature of the incoming charge may be kept within safe Internally-driven superchargers were used almost exclusively  in high horsepower radial reciprocating engines and are  engine driven through a mechanical connection. Although  their use is very limited, some are still used in cargo  carriers and spray planes. Except for the construction and  arrangement of the various types of superchargers, all  induction systems with internally driven superchargers  were very similar. Aircraft engines require the same air  temperature control to produce good combustion in the  engine cylinders. For example, the charge must be warm  Internally Driven Superchargers 3-6