How to Determine the RPM on a 15-HP Tiller Outboard Motor

A shop tachometer is used to determine how much rpm a 15-horsepower tiller outboard is producing, whether for setting the motor's timing or adjusting the low-speed idle. The tachometer uses the electrical pulses from your motor's ignition coil as the basis for its reading. It allows you to assess the changes in the motor's speed as you alter the motor's timing or low-speed idle.

Things You'll Need

  • Shop tachometer
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Instructions

    • 1

      Locate the gray wire in the wiring harness between the ignition control module and the ignition coil. The wire will be next to the purple and gray wires and has a bullet connector at its end.

    • 2

      Set the "Pulse" selector on a shop tachometer to "1." The 15-horsepower outboard is a two-cylinder engine, so the ignition coil will pulse once per crankshaft revolution.

    • 3

      Connect the alligator clip on the red lead of the shop tachometer to the bullet connector on the gray wire of the ignition module.

    • 4

      Connect the alligator clip on the shop tachometer's black lead to a ground on the powerhead.

    • 5

      Start the engine and read the number of rpm displayed on the shop tachometer.