Ryobi String Trimmer Repair

Updated February 21, 2017

Ryobi is a manufacturer of power tools, woodworking tools, and outdoor equipment such as string trimmers. The Ryobi string trimmer is powered by a small gasoline engine that drives a rotary head that contains a length of plastic line. When the line wears down from making contact with obstacles, the head can be tapped on the ground which feeds more line from the trimmer. The Ryobi string trimmer has many moving parts and will need maintenance and repair from time to time.

Press down on the latch on the plastic engine cover while simultaneously pulling the cover away from the engine to reveal the air filter screen. Clean the surface of the screen regularly with a soft bristle brush to keep the engine running properly and for engine longevity. Put back the cover by inserting the tabs on the cover into the slots on the base of the air cleaner assembly. Push the cover against the side of the engine until it snaps into place.

Locate the idle speed adjustment screw behind the plastic engine cover near the air filter. Remove the cover. Turn the screw slightly in a counterclockwise direction with a flat blade screwdriver if the trimmer cutting head spins while the engine is idling. Turn the screw until the head stops spinning and the engine is running smoothly. Replace the cover.

Locate the spark plug on the side of the engine cylinder head. Pull the spark plug wire straight off of the spark plug and push it aside. Press a spark plug wrench onto the end of the plug until it is fully seated. Twist the plug out of the engine in a counterclockwise direction. Check the gap between the grounding strap and the centre electrode of the plug with a spark plug gapping tool. Move the grounding strap in the direction needed with the notched end of the spark plug gapping tool so that the gap is .025 inch. Thread the plug back into the engine and tighten it with the spark plug wrench.

Loosen the full filler cap if the engine is running poorly. Replace the cap with a new one, which has a built-in non-replaceable filter, if engine performance improves when the cap is loosened.

Replace the string cutting head by first removing the spool retainer at the base of the head in a counterclockwise direction. Place the retainer aside. Pull the head straight off of the base of the trimmer. Push a new cutting head into place on the trimmer until it is fully seated on the driveshaft. Twist the retainer back into place hand-tight.


According to Ryobi, replace the spark plug with a new one annually. According to the Ryobi string trimmer owner's manual, the spark arrester and muffler exhaust port must be cleaned every 50 hours of use or annually, whichever comes first. The spark arrester may become clogged with carbon which may decrease the trimmer's power output. Ryobi recommends having this service performed by a qualified service technician.

Things You'll Need

  • Soft bristle brush
  • Flat blade screwdriver
  • Spark plug wrench
  • Spark plug gapping tool
  • Replacement fuel filler cap
  • Replacement cutting head
  • Spark plug (optional)
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