Symptoms
- Grass isn't being cut cleanly, just pushed over
- Engine sounds fine but cutting feels weak
- Line seems to just brush grass rather than cutting it
- Performance was better with a fresh spool of line
Likely causes
- CommonLine too short or worn thinLine that has worn short cuts less effectively and needs to be advanced or replaced.
- CommonDirty air filter reducing powerRestricted airflow reduces overall engine output, weakening cutting force.
- PossibleWrong line diameter for the jobThin line designed for light trimming struggles with thick or tall grass.
- PossibleOld, brittle lineLine left in the trimmer for a long time can become brittle and less effective at cutting.
- Less commonEngine running rich or lean, reducing powerA carburetor issue can rob the engine of power even if it starts and idles fine.
What to do
- Bump the head to advance fresh line, or manually rewind with new line if it's old or brittle.
- Check the air filter and clean or replace it if dirty.
- Confirm you're using the line diameter recommended for your trimmer model and the type of grass you're cutting.
- For thick or tall grass, consider using the largest line diameter your trimmer supports, or a heavier-duty head.
- Test cutting performance immediately after installing fresh line to establish a baseline.
- If performance is still weak with fresh line and a clean filter, check fuel freshness and mix ratio.
- Have the carburetor checked by a small-engine shop if power still seems low across all these fixes.
Tools and parts
- Replacement trimmer line
Trimmer lineSearch: “string trimmer line correct diameter”
When to call a pro
If fresh line, a clean filter, and fresh fuel don't restore cutting power, have a small-engine shop check the carburetor and engine.
Safety
Generally low risk
Generally low risk for a careful person. Stop if anything looks different from what this guide describes.