How to Test a Small Engine for Spark
If your small engine isn't starting, you'll need to diagnose many issues including the spark plug. This video walks you through the steps of how to test for a spark using a spark tester.
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The trimmer head stopped spinning when the motor was revved up, indicating either a bad centrifugal clutch or broken cable.
Remove three screws holding trimmer shaft to motor.
Spin trimmer cable with fingers to ensure trimmer head rotates, thus ensuring clutch is bad.
Remove spark plug and stuff nylon rope into motor cylinder to prevent motor shaft from rotating when applying torque to motor shaft.
Use impact wrench and Torx 20 screwdriver to remove one screw (CCW) that secures drum housing to motor shaft.
Remove drum and expose motor shaft.
Use adjustable wrench to remove old clutch (CCW).
Screw on new clutch (CW) using adjustable wrench to tighten.
Slip new washer over the motor shaft.
Slip new drum over motor shaft and tighten with Torq 20 screwdriver.
Reconnect trimmer shaft to motor and tighten three screws.
Remove the rope and replace the spark plug.
Start the motor and ensure trimmer head spins as motor revs up and clutch engages.