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Test 25 - Basic Ignition Timing Check

  1. Connect a tachometer and timing light to engine. Ground carburetor switch using a jumper lead. Start engine and let run until operating temperature is reached. Momentarily raise the engine speed above 1100 RPM. If equipped, disconnect and plug vacuum hose at solenoid kicker. Disconnect and plug vacuum hose at computer (engine RPM will drop when hose is disconnected).
  2. Engine idle speed should be below curb idle specifications. If necessary, turn idle screw to lower the engine RPM. Basic timing should be within 2° of specifications shown on emissions label. If basic timing is okay, proceed to step 3). If basic timing is not okay, adjust as necessary.
  3. Remove jumper lead from carburetor ground switch. Connect vacuum pump to computer and apply 16 in. Hg vacuum. Raise engine speed to 2000 RPM. Timing should be within 4° of specification. Refer to SPARK ADVANCE TEST SPECIFICATIONS  previously outlined in this article. If spark advance is okay, proceed to step 4). If spark advance is not okay, replace computer.
  4. Return engine to idle speed. Unplug vacuum hose to the computer and connect a vacuum gauge. Gauge should read manifold vacuum. If vacuum is okay, proceed to TEST 26  . If vacuum is not okay, check vacuum supply from carburetor.
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