Why is My String Trimmer Head Not Spinning Fast Enough?

When your weed eater’s trimmer head is not cutting the grass after a few seasons of use, it may be due to a lack of power for one of several reasons. Luckily, you can inspect the tool yourself to figure out whether there is a problem with the throttle, the clutch, the drive cable, or the trimmer head itself.

The Trimmer’s Power Source

Whether you have a Stihl, Ryobi, or Husqvarna string trimmer, the big differentiator among models will be the power type for the tool: electric or gas engines. Electric and battery powered weed wackers tend to not have the same problem with slow spinning that gas powered trimmers do. They either get the power they need, or they don’t.

Gas powered weed eaters, on the other hand, have more interchangeable parts that can wear down and need to be adjusted or replaced over time.

How Do I Fix My Trimmer Head’s Speed?

How Do I Fix My Trimmer Head's Speed

A string trimmer usually only has one speed, which is engaged by the throttle button on the handle. Your weed eater comes preadjusted when you buy it, so it should only need to be fixed if it’s going slower than normal. To fix the problem on your own, a good inspection will help diagnose where the problem is located.

The Drive Cable

When you push the throttle trigger on the handle, it engages the clutch, which allows the engine to deliver power to the spinner through the drive cable. If the trimmer head moves slowly, it’s receiving power from the engine, and the problem isn’t with the throttle. A broken or disconnected throttle cable will prevent the engine from accelerating at all.

The Trimmer Head

A few problems with the trimmer head may result in slowed performance:

  • The bump knob – When you have a stuck bump knob, or the bumper has been worn down from use, it can prevent the head from spinning correctly.
  • Disconnected drive shaft – There is a pivoting connection that spins the head at the end of the drive cable by rotating the attachment’s gears. Over time, if the head slips downwards from use, it can loosen the pivot from the socket in the head.
  • Worn internal gears – Gears inside the head are rotated by the pivoting drive shaft The gears in the trimmer head can wear down over time, making their connection looser and affecting the spinning power.

Should The Trimmer Head Spin At Idle?

While a few weed wackers may have slow, idle spinning, most don’t spin unless engaged by the throttle for safety reasons. If your trimmer continues to spin despite not holding the throttle button, the clutch may not be engaging correctly. The same may be true if the spinner doesn’t pick up speed once the throttle is triggered.

How Do I Know If My Trimmer Clutch Is Bad?

String Trimmer

A worn clutch can cause the trimmer to barely spin when you squeeze the throttle. If the bump knob, gearheads, and attachments are fine, you should inspect the engine’s clutch to see if it’s the cause of the slowing.

The clutch is a release that allows the engine to transfer power to the transmission or the drive cable when the throttle is pressed. The clutch itself can corrode or get worn down over time, or its spring mechanism can become stiff and prevent smooth rotation.

Over time, rust, corrosion, and pressure from movement can wear away at the metal clutch or the clutch shoe (a friction absorber). If the shoe or the clutch wears down, it may not make full contact when the throttle is engaged. This piece can be purchased and replaced easily, but sometimes a good sanding to remove corrosion can extend the part’s life. If it’s too worn down, however, it will be most effective to simply switch the old one out for a new one.