A bump-feed head that jams, feeds unevenly, or spits out both lines at once has usually been loaded wrong, not built wrong. The fix costs nothing and takes five minutes once you know the sequence — length, direction, tension, and how the ends seat in the eyelets.
Safety note. Always stop the engine and let the head come to a complete stop before opening it. Bump-feed heads have spring-loaded internals, and an engine left idling or a head still spinning while you work on it is an easy way to catch fingers or line in moving parts.
What you need before you start
- Trimmer line rated for your head — check the diameter printed on the head housing or in the manual, typically 2.0-2.7 mm for most domestic heads
- A length of line: most dual-line heads take roughly 4-6 m per spool (2-3 m per side), but this varies by head size — check the capacity marking on the spool itself
- No tools required for most consumer heads; some semi-pro heads need a small screwdriver or the head’s own retaining pin to lock the spool while you open it
| Head type | Typical line diameter | Typical length per fill |
|---|---|---|
| Light domestic dual-line | 2.0-2.4 mm | 4-5 m (2-2.5 m per side) |
| Standard homeowner dual-line | 2.4-2.7 mm | 5-6 m (2.5-3 m per side) |
| Semi-professional dual-line | 2.7-3.5 mm | 6-8 m (3-4 m per side) |
Step-by-step: loading the spool
- Stop the engine and confirm the head is fully stationary. Disconnect the spark plug lead on petrol machines or remove the battery on cordless ones if you’re at all unsure the head could still turn.
- Release the spool. Most heads use a press-and-twist cap, a pair of side tabs you squeeze inward, or a bump-knob you unscrew. Note how the cap seats — you’ll need to refit it the same way.
- Remove the old line remnant and clean out the housing. Grass juice and dried sap build up inside the spool cavity and around the eyelets; a dry cloth or a quick blast of compressed air clears it. Check the eyelets for grooving or a sharp edge — a worn eyelet will saw through new line at the same spot every time.
- Check the direction arrow moulded into the spool body. This tells you which way to wind, matching the head’s rotation. Winding against the arrow causes the coil to tighten on itself in use instead of paying out, and is one of the most common causes of a head that jams solid after a few bumps.
- Find the centre point of your cut length and hook or slot it at the spool’s centre divider (most dual-line spools have a notch, tab, or small hole for this — check yours, some single-line heads load differently).
- Wind both halves evenly and simultaneously in the arrow’s direction, keeping the line under light hand tension. Lay each wrap flat against the previous one rather than letting turns cross over — crossed or loose turns are what cause line to bind, weld together under friction heat, or feed unevenly line-to-line.
- Leave the last 10-15 cm of each end free and clip it into the retaining slots on the spool rim (small notches or a single narrow gap on most heads) to stop the coil unwinding before you close the head.
- Thread each free end through its eyelet from the inside out, pulling gently until the retaining slot releases the line — on most heads this happens naturally as you refit the cap and give the ends a firm outward pull.
- Refit the spool and cap in the housing, making sure any drive tabs or springs line up as they were before you opened it, then press or twist to lock it home.
- Pull both ends until they release fully from the retaining slots and sit at roughly equal length, then trim to the length recommended for your head (usually marked by a cutting guide on the guard).
Safety note. Before starting the engine, spin the head by hand if it’s accessible and check both lines move freely and evenly. A head that binds by hand will bind — or throw a line unevenly — under power, and an unbalanced head at cutting speed causes vibration that’s uncomfortable at best and can loosen other fasteners at worst.
Common loading mistakes and what they cause
| Mistake | What happens |
|---|---|
| Overfilling past the rated capacity | Coil binds under its own spring tension; head won’t bump-feed at all |
| Wound against the direction arrow | Line tightens on itself while running instead of releasing |
| Crossed or loose overlapping turns | Line welds to itself from friction heat, or feeds unevenly |
| Line too thick for the head | Won’t pass through eyelets or release from the bump mechanism |
| Line too thin for the head | Feeds too easily, wears fast, breaks off under load on tougher growth |
| Worn or grooved eyelet not checked | New line saws through at the same weak point within minutes |
When both lines won’t feed evenly
If one side feeds and the other doesn’t, the usual cause is uneven tension during winding — one half wound tighter than the other, or the centre point wasn’t accurately found before you started. Unwind and redo it, checking the centre notch or hole is genuinely centred before winding both sides together. A head that fed evenly before but has started favouring one side is more often a sign of a worn eyelet or a weak return spring than a loading fault — worth checking the spring’s bump-and-return action against a known-good head if you have one to compare.
Checklist before you cut
- Line diameter matches what’s specified for your head
- Wound in the direction of the moulded arrow, not against it
- Both halves wound evenly, flat, under light tension, no crossed turns
- Ends seated correctly through the eyelets, not pinched or kinked at the housing
- Spool cap or tabs fully locked home, no play or rattle
- Head spins freely by hand with both lines moving before you start the engine
When to call a dealer
If you’ve reloaded the head correctly two or three times and it still won’t feed, jams immediately, or feeds unevenly regardless of technique, the problem is very likely in the head itself rather than the line — a weakened or broken return spring, a worn bump button mechanism, or a cracked internal spool are all common failures on older heads and usually cheaper to replace as a head assembly than to have repaired. Also get a dealer to look at it if an eyelet has worn through to a sharp edge or a groove deep enough to catch a fingernail — a damaged eyelet will keep cutting through new line no matter how well it’s loaded, and eyelets aren’t always sold as a separate replaceable part on every head design.