String Trimmer Line Won't Feed? What to Do

Part of our complete Small Engine Troubleshooting Guide.

This is the list for a trimmer that runs but will not pay out line. If it will not start in the first place, our guide to a handheld two-stroke that will not start is the right place to begin instead. Work down this list in order, because the free answers sit at the top of it.

1. Which Head Do You Have?

Answer this first, because the two kinds pay line out for different reasons. A bump head releases a measured length only when the knob taps firm ground with the engine at working speed, so a gentle tap on soft grass gives you nothing and reads as a fault when nothing is wrong.

An automatic or speed-feed head advances on a change in engine speed instead, which means it needs the throttle worked rather than the head knocked. Trying to bump an automatic head, or tapping a bump head too softly, accounts for a fair share of the trimmers that come in here feeding perfectly.

2. The Line Itself

More heads are stopped by the line than by anything inside them. Four things to look at before you blame the mechanism:

• The wrong diameter. Use the size the machine calls for. Heavier line lugs the engine, wears the clutch and binds in the eyelets.
• Line that sat a season. It dries out and goes brittle, then snaps off inside the head instead of paying out.
• Welded coils. A spool left in a hot shed or run hard can fuse its own turns together, so the line cannot slide.
• Overfilled. Wound past the rim of the spool, the coils press on the cover and nothing moves.

3. How It Was Wound

If the line is right, the wind is the next suspect and the most likely single cause of all. Crossed coils are the classic one: a turn that crosses over itself traps everything behind it, and the head locks solid on the first tap. Loose winding does the same thing more slowly, because slack coils collapse into each other under load.

Wind in the direction the arrow on the spool shows, keep the turns tight and lying parallel, stop level with the rim, and seat both ends in the notches so they cannot fall back in while you refit the cover. Soaking a brittle spool of line overnight makes it behave while you wind it. Our leaf blower and trimmer tune-up guide covers this alongside the rest of the end-of-season service.

4. The Head Hardware

With the spool out, look at the parts the line has to pass through and the parts that let it move:

• The eyelets. Line running through them at speed saws a groove in the metal, and that groove grabs and shears line instead of releasing it.
• The bump knob. Worn thin or worn through, it no longer lifts the spool against its spring, so a tap does nothing.
• The feed spring. Stretched, missing or fitted the wrong way round, it cannot return the spool to index on the next tap.
• Packed debris. Grass juice and dust set hard behind the spool and hold it where it is.

5. A Head That Is Not Reaching Speed

Centrifugal force is what throws the line out. If the head is not spinning fast enough, a perfect wind in a perfect head still will not feed, and that sends people back to the spool over and over looking for something that was never wrong.

Three things slow a head down. A clutch that slips lets the engine rev while the shaft lags, usually with a smell of hot metal. A gearhead on a curved-shaft machine that has run dry gets hot and noisy and robs speed. And a shaft bent by a drop or a snagged fence binds in its housing. All three are worth hearing rather than guessing at: an engine climbing in revs with no matching whine from the head is the tell.

6. Line That Breaks Off Every Time

This looks like a feed fault from the seat of the pants, because you keep tapping and keep running out, but the line is going out and then being destroyed. Fences, concrete edges, rock and tree bark take the end off faster than the head can pay it out.

A cutting length that is too short does it as well: with only an inch or two out, the end runs in the hottest, fastest part of its arc and cooks. Let it out to the length the guard allows, keep the head off the ground rather than resting it as you walk, and watch for the welded-end look that says the line is being melted rather than cut.

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Matching the Symptom to the Cause

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When to Call the Shop

Rewinding a spool, fitting the right diameter line, clearing packed grass from behind it and replacing a worn bump knob are all driveway jobs, and between them they account for most of the trimmers that get carried in here for not feeding. If the head comes apart cleanly and the wind looks right afterwards, you have very likely fixed it yourself for the price of a spool of line.

Bring it in when the eyelets have worn into the housing, when a fresh wind in a good head still will not pay out, when the head sounds slow or hot, or when a curved-shaft gearhead has gone noisy. A dry gearhead, a slipping clutch and a bent shaft are bench jobs, and they are also the three that get expensive if a machine is run on for a few more weekends.

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String Trimmer Line Feed FAQ

I tap the head and no line comes out at all. Where do I start?
Open the head and look at the winding before anything else. Crossed or slack coils are the most common cause by a wide margin, and a rewind costs nothing but a few minutes.

How do I know what line my trimmer takes?
The diameter is in the manual and often stamped on the head itself. Use that size: heavier line drags on the engine, wears the clutch and will not pay out cleanly.

The line snaps off at the head every time I use it.
Usually the eyelets have worn into a groove that bites the line, or it is being run against concrete and fences. Brittle line that sat through a season does it too.

Do you repair trimmer heads in Richmond, KY?
We do, across Madison County. We rewind spools properly, service heads and gearheads, and you get a firm quote before any work begins: (859) 661-8877.