How to String a Bump-Feed Weed Eater

To string a bump-feed weed eater, disconnect power, open or access the head, remove leftover line, and wind fresh trimmer line the way the spool arrows point. Thread the ends through the eyelets, reassemble the bump knob, and tap-test that a bump feeds a short length without dumping or jamming. Wind direction, line diameter, cut length, and open-spool versus through-the-head loading vary by model—use the marks on your head or the manual.

How a bump-feed head works

A bump-feed weed eater is a string trimmer whose cutting head stores coiled trimmer line on a spool and releases more of that line when you tap the bump knob on the ground while the head is spinning. The spool sits in a housing with one or two eyelets. A spool spring, or a similar retainer, keeps the spool seated so line cannot unwind freely. A bump briefly unseats or indexes the spool. Centrifugal force then pulls a short additional length out through the eyelets, after which the retainer catches the spool again.

That tap-to-feed design is what you are restoring when you restring the head. If the coil is wound the wrong way, piled loosely, or overfilled, the spool cannot slip a controlled length. The usual results are a dead head that will not feed, a dump that empties the spool in one burst, or line that welds itself from friction heat.

A bump-feed head is not the same as a fixed-line head or an automatic-feed head. Fixed-line heads use pre-cut pieces pressed or clipped into slots; there is no spool to wind and no bump knob to tap. Automatic-feed heads try to advance line without a bump, often by centrifugal action or another internal mechanism. Some housings look similar from the outside, so do not assume a neighbor’s loading method matches yours. Treat the rest of this article as model-agnostic: identify the marks on your own head, then follow them.

Before you take anything apart, name the parts you will handle. The spool is the drum that holds the coil. The bump knob is the button or cap you tap on soil or dense grass. Eyelets are the metal or reinforced openings the line exits through. The spool spring usually sits under or around the spool and can launch when the cap comes off. The housing may also have alignment tabs, a center divider on a dual-line head, and a debris shield on the shaft with a cut-off blade that trims line that is too long.

Make the trimmer safe before you touch the head

Do not service a head that can still start. Isolate the tool completely, then wait until every rotating part has stopped. Hands, eyes, and face will be close to a spring-loaded cap and to leftover line that can snap or fling debris.

• On a gas string trimmer, stop the engine and pull the spark-plug boot off the plug so a pull of the starter cannot fire the engine.
• On a battery trimmer, remove the battery pack from the tool. Do not rely on the trigger lock alone.
• On a corded trimmer, unplug the power cord from the outlet and from the tool if the cord detaches.
• Wait until the head is fully still. Residual spin can cut skin or yank line through an eyelet.
• Wear eye protection whenever you open the head and whenever you later restore power for a bump test.

Point the bump knob away from your face when the cap comes off. A hidden spring can pop toward you, and a tight snap-tab cap can jump. If the tool was just running, let the head cool enough to handle. Work on a bench or a tarp so a washer, spring, or tab cannot disappear in grass. Never open, wind, or reassemble the head while the tool still has a battery installed, a plug boot connected, or a live cord attached.

If the housing is cracked, the bump knob is shattered, or you cannot tell how the cap retains the spring, stop and consult the owner’s manual or a qualified small-engine or outdoor-power technician. Forcing a damaged head closed is not a safe workaround.

Identify your head and how it loads

Two common consumer families exist, and they are not interchangeable in method. One family requires you to remove the bump cap, lift out the spool, and wind line onto that spool. The other accepts a through-the-head load: you feed a single length of line in one eyelet, through a channel or slot in the spool, and out the opposite eyelet, then twist the bump knob or spool to take up the line without a full teardown. Some heads also advertise a speed-load style path that is still a through-eyelet method. None of these families is universal. Look at your housing instead of copying a video for a different brand.

Inspect the bump cap. Many consumer caps pry off at molded snap tabs; others unscrew. If you see no seam and the bump knob turns independently of the housing, you may have a through-the-head design. Next inspect the spool, if you can see it or after you lift the cap. A single-line head has one winding path. A dual-line head usually has a center divider or two separate channels so two tails exit opposite eyelets. Loading a dual-line spool as if it were a single pile of line is a common cause of uneven feed.

Find the molded winding arrows, the line-diameter stamp, and any alignment tabs or index marks on the spool and housing. Those marks override generic “always clockwise” advice. Clockwise is not always correct. If arrows and size stamps are missing, worn off, or contradictory, use the owner’s manual rather than guessing. Guessing the wind direction is how people create a head that looks freshly strung and still will not bump.

Choose trimmer line that fits this head

Correct line diameter is marked on many heads, on the debris shield, or in the manual. Use that mark. Too-thick line may not pass the eyelets, may not seat in the spool channel, and can overload a small consumer head. Too-thin line breaks sooner and may slip through retainers so the coil dumps. Those are mechanical limits, not a promise that any one diameter will last longer or cut faster.

Shape matters more for feeding than marketing copy suggests. Round line often travels through eyelets with less snagging. Twisted, serrated, or multi-sided line can cut vegetation differently, but the extra edges can also catch in worn eyelets or stack unevenly on the spool. If your head already struggles to feed, start with the diameter stamped on the tool and a simple round profile before you experiment with specialty shapes.

More line is not always better. An overfilled spool binds against the housing, so a bump cannot release anything. Crossed or loosely piled line does the same. Cut only as much as your spool can hold in flat, side-by-side windings with room for the cap to close flush. There is no single footage that fits every bump-feed head, so do not treat a number printed on a random package as a factory spec for your tool. If the package lists several diameters, match the stamp on your head rather than buying the thickest option “for power.”

Remove leftover line and open the head

With power isolated and eye protection on, clear the old coil before you add new line. Short, fused, or welded leftover ends will not splice cleanly into a new winding. They create lumps that lock the feed. Pull them out and discard brittle pieces.

For a removable cap, support the housing in one hand and release the snap tabs with a flat tool if needed, or unscrew the cap if that is how your head is built. Do not assume every cap unscrews the same direction. Work over a tray. As the cap lifts, keep a thumb over the opening so the spool spring cannot fly out. Note the spring’s orientation—which end faces the spool, which end sits in the housing—before you set it aside. A reversed spring is a frequent reason a freshly closed head will not bump.

Lift the spool straight out. Photograph or sketch the way any washer, retainer, or alignment tab sat if the stack is not obvious. Pull remaining line off the spool. If ends are melted into a lump inside an eyelet, work them out carefully rather than prying the eyelet open. Oval, cracked, or missing eyelets, a cracked housing, or a flattened bump knob are wear problems restringing will not fix. Flag those parts for replacement after you finish assessing the head. Do not force a cracked cap back on.

For a through-the-head load, you may not need a full teardown. Pull the old tails out through the eyelets until the path is clear. If line is welded inside the channel, then open the housing using the same spring-aware method so you can clear the jam instead of pushing new line into a blocked path.

Cut, insert, and wind the line the marked way

The only stable direction rule is this: follow the molded winding arrows on the spool or housing. Winding against the arrows is a leading cause of no-feed and of dump-out. Keep each turn flat, taut, and side-by-side. Crossed windings and loosely piled figure-eights lock the coil so a bump does nothing, or they let the whole coil slough off at once.

Open-spool wind on a dual-line or single-line head

On a typical dual-line head with a center divider, either fold one length in half and seat the midpoint in the center slot, or cut two similar lengths and anchor each side in its own slot, depending on how your spool is molded. Keep both halves similarly loaded so the head stays balanced and both eyelets can feed. On a single-line head, anchor one end in the spool’s slot or hole and wind only that path.

Wind in the arrow direction until the spool is full enough to feed for a reasonable session but not so full that the last turns climb over the flanges or rub the housing. Leave tails long enough to reach and pass through the eyelets after the spool goes back in the housing. Do not publish a universal cut length here, because spool capacity varies. If you overshoot, you can trim tails after a test spin at the debris-shield cut-off blade. Tails should be short enough not to slap the guard continuously before that test, but long enough that they cannot slip back inside the housing.

Through-the-head load

Align the spool’s through-channel with both eyelets. Many heads have an index mark or a window that shows when the path is open. Push one continuous piece of line in one eyelet until it exits the other. Center the length so both sides are similar, then turn the bump knob or the marked winder in the arrow direction so both tails shorten evenly. Stop when the remaining tails are long enough to cut vegetation but not so long that they sit against the debris shield before you test. If the knob will not turn, the channel is not aligned or leftover line is still blocking the path—do not force it.

Thread the eyelets and put the head back together

Line must exit the actual eyelets. Drain holes, screw bosses, and alignment openings are not feed paths. If ends sit inside the housing, centrifugal force cannot pull line out and a bump will feel dead.

Seat the spool so its notches or lugs engage the housing slots. Replace the spool spring in the same orientation you noted. Index the bump knob so any tabs, square drives, or cam faces match the spool. Lower the cap straight on. A cap that will not snap or screw down flush is misaligned, overfilled, or missing a part. Take it apart and reseat. Do not run a head that is only partly latched.

Confirm both tails (or the single tail) protrude from the eyelets and that the bump knob can move the small amount it needs to bump. If your debris shield has a cut-off blade, you can let leftover length meet that blade after a careful test spin rather than inventing an exact sticking-out measurement. Missing springs, reversed knobs, unseated tabs, and cracked housings are reasons to stop, not reasons to start the tool and “see if it holds.”

Test that a bump feeds line

Restore power only after the head is fully closed and the debris shield is installed. Put eye protection back on. Choose open space away from people, glass, and loose gravel. Start the trimmer the normal way for that tool, bring the head up to cutting speed, and give the bump knob a light tap on soil or dense grass—not on concrete if you can avoid it, because hard surfaces wear the knob faster.

A successful bump releases a short additional length while the head is spinning. You should not see the entire coil fly out, and you should not see zero movement after several firm taps. There is no universal inches-per-bump figure to chase. If nothing feeds, or if the spool dumps, shut the tool down, isolate power again, and rewind. Do not keep running a jammed head; slipping line in the eyelets is how coils weld to themselves.

After a good feed, let any extra length meet the cut-off blade on the debris shield. Listen for a harsh rattle or a lopsided whoosh that can mean one side of a dual-line head is much longer than the other or that the spool is not seated. Shut down and correct that before you return to tall grass. Never test with the shield removed and never disable the cut-off blade to keep longer line.

Fix common feed problems

Most bump-feed failures after a restring are winding or wear issues, not mysterious internal clutches. Rewind first, then inspect parts.

• Line will not advance when bumped. The coil was wound against the arrows, the spool is overfilled, windings are crossed, the diameter is too large for the eyelets, the spool is not indexed to the knob, or the spring is missing or inverted. Open the head, confirm arrow direction, and rewind flat and taut.
• The spool empties in one burst. Windings were loose, the line is too thin for the retainers, a tail was never captured in a slot, or the bump knob and spring are not catching the spool after the tap. Rewind more tightly and verify the spring stack.
• Line welded to itself or to the spool. The head was run while line slipped in the eyelets or while a jam prevented feed. Heat from friction fused the nylon. Discard the welded coil; do not pick at it and reuse the lump. Check eyelets for grooves that encourage slip.
• Only one side of a dual-line head feeds. The two halves were loaded unequally, one tail missed its eyelet, or the divider was ignored so both lengths sat on one side. Reload both channels similarly.
• The cap will not stay on or the head feels loose. Tabs are broken, the knob is worn flat, or the housing is cracked. Restringing will not restore a broken retainer.

Worn eyelets that have gone oval cut line and snag shaped profiles. A missing spool spring or a cracked bump knob removes the very mechanism that meters line. Those are replacement problems. Do not assume a homemade shim or extra wrap of tape returns a broken housing to reliable strength. If you cannot match line size or wind marks after a careful look, use the manufacturer’s parts information rather than improvising a different head type as a guaranteed fit.

Know when the head, not the line, needs replacing

Keep restringing only while the housing, eyelets, bump knob, and spring can still do their jobs. Visible defects that restringing will not fix include a cracked or melted housing, oval or missing eyelets, a flattened or broken bump knob, a lost or permanently deformed spool spring, and alignment tabs that no longer hold the cap. A head that repeatedly dumps or welds line after a correct rewind is often worn, not “picky about line.”

Stay with the original head type if you cannot identify a compatible replacement. Open-spool, dual-line, single-line, and through-the-head designs are not automatically interchangeable on the same shaft. If marks are gone and the manual is missing, look up the tool’s model number in the manufacturer’s parts information rather than buying an unrelated head and hoping the threads or snap ring match. A qualified outdoor-power shop can confirm fit when the housing is damaged or the mounting is uncommon.

Once the replacement head is on, treat it like the first restring in this article: isolate power, read the new arrows and diameter stamp, wind flat in the marked direction, exit the eyelets, close the cap fully, and bump-test with the debris shield and eye protection in place. That sequence—not a universal length or a universal clockwise myth—is what makes a bump-feed weed eater cut again.

Frequently asked questions

Can I mix leftover old line with a new coil?

No. Short or brittle leftover ends create lumps and weak joints. Pull the old line out completely and start a clean coil so the spool can slip evenly when you bump.

Why do some heads load without taking the cap off?

Those are through-the-head or similar speed-load paths. Line goes in one eyelet, through the spool, and out the other, then you wind with the knob. If your head has no through-channel, do not drill one. Open the spool and wind it the marked way instead.

Is clockwise always the correct wind?

No. Follow the winding arrows on your spool or housing. If the arrows are gone, use the owner’s manual. Winding the wrong way is a common reason a bump does nothing or dumps the whole coil.

Do I need the debris shield on for a bump test?

Yes. The shield protects you from debris and broken line, and its cut-off blade trims tails that are too long. Do not test a powered head with the shield removed.