The  PICKUP  COIL  OHMETER  TEST  compares actual   pickup   resistance   with   the   manufacturer’s specifications. If the resistance is too high or low, the pickup coil is faulty. To perform this test, connect the ohmmeter  across  the  output  leads  of  the  pickup  coil. Wiggle  the  wire  to  the  pickup  coil  and  observe  the meterreading. This will assist in locating any breaks in the  wires  to  the  pickup.  Also,  using  a  screwdriver, lightly tap the coil. This action will uncover any break in the coil windings. Pickup   coil   resistance   varies   between   250   and 1,500 ohms, and you should refer to the service manual for  exact  specifications.  Any  change  in  the  readings during the pickup coil resistance test indicates the coil should be replaced. Refer to the manufacturer’s service manual   for   instructions   for   the   removal   and replacement of the pickup coil. Once the pickup coil has been replaced, it will be necessary to set the PICKUP COIL AIR GAP. The air gap is the space between the pickup coil and the trigger wheel tooth. To obtain an accurate reading, use a NON- MAGNETIC FEELER GAUGE (plastic or brass). With one tooth of the trigger wheel pointing at the pickup  coil,  slide  the  correct  thickness  non-magnetic feeler gauge between the trigger wheel and the pickup coil. Move the pickup coil in or out until the correct air gap is set. Tighten the pickup coil screws and double- check the air gap setting. Ignition Timing The  ignition  system  must  be  timed  so  the  sparks jump  across  the  spark  plug  gaps  at  exactly  the  right time. Adjusting the distributor on the engine so that the spark  occurs  at  this  correct  time  is  called  setting  the ignition timing. The ignition timing is normally set at idle or a speed specified by the engine manufacturer. Before measuring engine timing, disconnect and plug the vacuum advance hose going to the distributor. This action prevents the vacuum advance from functioning and  upsetting  the  readings.  Adjustment  is  made  by loosening the distributor hold-down screw and turning the distributor in its mounting. Turning   the   distributor   housing   against   the distributor shaft rotation ADVANCES THE TIMING. Turning  the  distributor  housing  with  shaft  rotation RETARDS  THE  TIMING.  Refer  to  figure  2-53. When  the  ignition  timing  is  TOO  ADVANCED, the engine may suffer from spark knock or ping. When ignition  timing  is  TOO  RETARDED,  the  engine  will have  poor  fuel  economy  and  power  and  will  be  very Figure 2-53.—Determining the direction of rotor rotation. sluggish  during  acceleration.  If  extremely  retarded, combustion  flames  blowing  out  of  the  open  exhaust valve  can  overheat  the  engine  and  crack  the  exhaust manifolds. A timing light is used to measure ignition timing. It normally  has  three  leads—two  small  leads  that  connect to the battery-and one larger lead that connects to the NUMBER  ONE  spark  plug  wire.  Depending  on  the type of timing light, the large lead may clip around the plug   wire   (inductive   type),   or   it   may   need   to   be connected  directly  to  the  metal  terminal  of  the  plug wire (conventional type). Draw  a  chalk  line  over  the  correct  timing  mark. This will make it easier to see. The timing marks may be either on the front cover in harmonic balance of the engine, or they may be on the engine flywheel. With the engine running, aim the flashing timing light  at  the  timing  mark  and  reference  pointer.  The flashing  timing  light  will  make  the  mark  appear  to stand still. If the timing mark and the pointer do not line up, turn the distributor in its mounting until the timing mark  and  pointer  are  aligned.  Tighten  the  distributor hold-down screw. CAUTION Keep your hands and the timing light leads from the engine fan and belts. The spinning fan and belts can damage the light or cause serious personal injury. After the initial ignition timing, you should check to see if the automatic advance mechanism is working. This can be done by keeping the timing light flashes 2-42