My WetJet 300 Jet Ski Has No Spark

The WetJet Duo 300ZX was introduced by Mastercraft in 1995, the second year they built a personal watercraft. The Duo 300ZX was powered by a 70-horsepower, 701 cc Yamaha two-cylinder, two-stroke engine. Chasing down the reason this engine lacks a spark is a straightforward process that begins at the spark plugs and ends at the spark plug, with a side trip to the kill switch.

Things You'll Need

  • Digital multimeter
  • Battery charger
  • Spark tester
  • Kill switch
  • Starter switch
  • Wire gauge
  • Foot-pound torque wrench
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Instructions

    • 1

      Inspect all wiring for loose connections, damaged insulation and frayed wires. Replace wiring and tighten connections as necessary.

    • 2

      Set the multimeter for DC voltage. Ensure that the lock plate on the "Engine Stop" lanyard is in place. Place the red probe on the positive battery terminal -- marked with a "plus" sign -- and the black probe on the negative battery terminal, marked with a "minus" sign. The voltage should range between 11.1 VDC and 14.3 VDC. Charge the battery, using a battery charger, if the voltage reading is less than 11 VDC, and then recheck the voltage.

    • 3

      Remove the spark plug lead from the No. 1 spark plug. Connect the plug lead cap to a spark tester. Set the gap on the spark tester to 0.39 inches. Press the "Start" button and watch the spark through the tester's discharge window. If there is no spark, trace the positive cable from the battery to the 10 amp fuse in the fuse block.

    • 4

      Turn a digital multimeter to test continuity. Place the red probe on the side of the "battery side" of the 10 A fuse. Place the black probe on the kill switch's terminal with the red wire. If the resistance is less than 10 ohms, follow the brown wire to the terminal on the starter switch and move the red probe to that terminal. If the resistance is less than 10 ohms, the kill switch and fuses are in order. If not, replace the kill switch. Repeat the spark test, using the spark tester.

    • 5

      Place one of the multimeter's probes on each of the two terminals of the starter switch and press the "Start" button. If the resistance is greater than 10 ohms, replace the switch.

    • 6

      Set the digital multimeter to test resistance. Unplug the ignition coil lead and spark plug lead from one of the ignition coils. Place the red probe in the ignition coil lead terminal and the black probe in the spark plug lead terminal. Resistance should be 0.36 ohms or less. Move the red probe to the body of the coil. Once more, resistance should be 0.36 ohms or less. If not, replace the coil. Repeat for both ignition coils. Repeat the spark test.

    • 7

      Disconnect the No. 1 spark plug lead from the capacitor discharge ignition -- or CDI -- unit. Insert one multimeter probe into each end of the plug lead. Resistance should range between 6,100 and 14,300 ohms. Repeat for the No. 2 lead, where the resistance should range between 4,600 and 11,100 ohms. Replace the lead, if either spark plug lead is out of specification. Repeat the spark test.

    • 8

      Remove and replace the CDI unit, if the engine still fails to produce a spark. Remove the spark plugs with a plug wrench, if the engine fails to crank. Use a wire gauge to check the gap on two new spark plugs -- the correct gap is 0.39 inches. Install the new plugs and tighten to 18 foot-pounds, using a foot-pound torque wrench.