Quantcast FUEL SYSTEM - TM-5-3895-360-13_16

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TM 5-3895-360-13 1-12.  STARTER. The starter rope is wound around a pulley. As the rope is pulled, the pulley is turned clockwise, The dog retainer and spring holding the dogs in the cutouts of the pulley hub allow the dogs to move out of the retracted position. The sharp edges of the dogs dig into the side of the start- er  cup.  The  flywheel  turns,  providing  the  starting  force.  As the  rope  is  released,  the  dogs  retract,  allowing  the  rope to automatically rewind on the pulley. 1-13. FUEL SYSTEM. The fuel system is operated by crankcase pressure and vacuum pulses from the engine crankcase. The pulses are transferred to the fuel pump diaphragm causing fuel to be pulled through the inlet flipper of the pump and then through  the  outlet  flipper  of  the  pump. The carburetor is a demand-type carburetor. No fuel flows to the engine until the engine is cranked or operat- ing.  Lower  pressure  in  the  throttle  bore,  or  venturi,  causes the main metering diaphragm to depress the inlet liner. This allows the inlet needle to unseat and permits fuel to fill the fuel chamber. Fuel flows through the calibrated holes for low speed or the nozzle for high speed, based on engine demand and throttle shutter opening, The fuel pump aids fuel flow by furnishing larger quantities of fuel to the engine than would be possible without a fuel pump. The fuel pump cannot move fuel unless the fuel tank is vented. Fuel  flow  through  supply  openings  depends  partly  on main (high) or idle (low) adjustment needle settings. Fuel flow through discharge ports varies with the position of the throttle shutter. The throttle shutter blocks off or ex- poses ports to the engine demand and determines the mode of operation. Fuel flow is enhanced by the throttle bore, or venturi, a narrowing in opening that causes air to flow faster and a drop in pressure. a. b. Starting Choke Operation. During starting choke operation, the choke shutter is closed and the throttle shutter is open. The fuel passes through main,  primary  idle,  and  secondary  idle  fuel  dis- charge  ports. Idle Operation. During idle operation. the choke c. d. Intermediate  Operation.  During  intermediate  oper- ation,  the  choke  shutter  is  open  and  the  throttle  shut- ter  is  open  approximately  halfway.  Engine  speed and air flow increase as the throttle shutter opens. The  amount  of  fuel  delivered  increases  as  the  throttle shutter  uncovers  the  secondary  discharge  port,  ex- posing it to engine suction. High Speed Operation. During high speed opera- tion, the choke shutter and the throttle shutter are open. The amount of fuel delivered reaches a maxi- mum when the throttle is fully open. All discharge ports  are  fully  exposed  to  engine  demand  and  to venturi  effect. 1-14.  REED  VALVE  ASSEMBLY The reed valve is between the carburetor and the crank- case of the engine. It times the injection of the fuel and air mixture from the carburetor into the crankcase. The reed valve opens only when pressure in the crankcase drops to a predetermined point on the compression stroke. The                reed  valve  maintains  contact  with  the  reed  plate  until pressure changes in the crankcase. Reed valve travel away from the plate is limited by the reed stop. When crankcase  pressure  increases,  the  built-in  spring  action of the reed valve returns and holds it against the plate. 1-15.  IGNITION  SYSTEM. The ignition system consists of six major components: the  flywheel,  condenser,  coil,  breaker  points,  ignition  or shorting  switch,  and  spark  plug. The rotation of magnets along the outer edge of the fly- wheel creates a rotating magnetic field that cuts through the coil winding, building a very strong magnetic field. As the magnets pass the coil, the magnetic field collapses, sending a high voltage charge to the spark plug. shutter is open and the throttle shutter is slightly open. This prevents fuel from passing through the secondary idle discharge port. 1-8


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