How to Check the Speed Sensor on a Yamaha FX140

Owning a Yamaha WaveRunner FX140 means maintenance and repair. As is the case with so many electronic parts, diagnosis is pointless, since the unit can't be serviced. This means that, when you notice the speedometer is giving you wacky readings -- it might tell you you're going 5 mph when you're clearly moving at a faster clip -- it's time to replace the speed sensor.

Things You'll Need

  • 2 adjustable wrenches
  • FX140 speed sensor replacement kit
  • Gasket compound
  • Thread locker
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Instructions

    • 1

      Push the nose of the jet ski against your workshop wall, if you're working with the ski off the trailer. Lift the back of the FX140 -- the stern -- and set it up on jack stands. If the FX140 is on its trailer, slide it back until the rear third of the ski is hanging over the end of the trailer, then slide the jack stands beneath it for added security.

    • 2

      Locate the "ride plate" -- the plate bolted onto the bottom, rear of the FX140's hull. It covers the bottom of the jet pump nozzle; at its rear edge, you'll see a small paddle wheel: that's the speed sensor transmitter. It's turned by the water as the jet ski moves through the water and sends a signal to the sensor. The sensor then converts the paddle wheel's rotation to the jet ski's speed-through-the-water.

    • 3

      Slide an adjustable wrench between the ride plate and the jet nozzle and latch onto the nut -- one of the six that hold the sensor and paddle wheel in place on the ride plate. Position a second adjustable wrench on the hex head of the bolt on which the nut is threaded.. Use the wrench on the outside of the vessel to remove the bolt, while the second wrench holds the nut -- on the inside of the vessel's ride plate -- steady.

    • 4

      Pull the paddle wheel, sensor unit and grommet from the bottom of the ride plate. Scrape any grommet material from the ride plate with a putty knife.

    • 5

      Unplug the the terminal with the red and white wire from the left side -- as you face the WaveRunner -- of the speed sensor. Unplug the terminal with the black wire and the yellow wire from the right side of the terminal.

    Speed Sensor Installation

    • 6

      Plug the terminal with the red and white wire into the left side of a new sensor. Plug the termainal with the yellow wire and the white wire into the right side of the new sensor.

    • 7

      Apply gasket compound to the grommet found in the paddle wheel/speed sensor replacement kit. Settle the grommet onto the top of the lip of the paddle wheel unit. Apply thread locker to the speed sensor mounting bolt threads.

    • 8

      Press the paddle wheel and sensor unit back into the opening on the ride plate. Fit the mounting bolt through the bore in the paddle wheel and sensor unit.

    • 9

      Fit the nut onto the bolt and tighten the bolt with one wrench while steadying the nut with the other.