Toro 51978 User Manual

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17 in. String Trimmer - Curved Shaft

Item No. 51958— 319000001 & Up

18 in. String Trimmer - Straight Shaft

Item No. 51978— 319000001 & Up

Item No. 51978A— 319000001 & Up

English (EN), French (FR), and Spanish (ES)

WARNING:

To reduce the risk of injury, the user must read and understand the operator’s manual. Save this manual.

Form No. 3427-359 Rev. A

If you have questions concerning

your trimmer, please call us

at 866-574-9242 (US) or

866-574-9243 (Canada).

NOTICE

Do not use E15, E20 or E85 fuel in this

product. It is a violation of federal law

and will damage the unit and void your

warranty. Only use unleaded gasoline

containing up to 10% ethanol.

Table of Contents

Questions and Answers:

N
nserranoAug 9, 2025
Why my Toro Trimmer engine will not start?
- W
  William NguyenAug 9, 2025
  If your Toro Trimmer's engine won't start, there could be several reasons. First, check for spark by removing the spark plug, reattaching the cap, and laying it on the metal cylinder. Pull the starter cord to look for a spark at the tip. If there's no spark, try again with a new spark plug. Another reason could be lack of fuel. Push the primer bulb until it's full; if it doesn't fill, the fuel delivery system might be blocked. Alternatively, the engine might be flooded. Remove the spark plug, turn the trimmer so the spark plug hole faces the ground, ensure the choke is set to RUN, and pull the starter cord 10-14 times to clear excess fuel. Clean and reinstall the spark plug, then try starting again with the trigger fully depressed.
C
Cynthia GallegosAug 15, 2025
How to fix Toro 51978 engine that does not reach full speed and emits excessive smoke?
- M
  Michele KaufmanAug 15, 2025
  If your Toro Trimmer engine doesn't reach full speed and emits excessive smoke, make sure that you are using fresh fuel and the correct 2-cycle lubricant mix. Also, check and clean the air filter. Finally, clean the spark arrestor screen.
S
Stephanie MejiaAug 21, 2025
What to do if the line will not advance when using automatic line lengthening on Toro 51978?
- J
  James CarsonAug 21, 2025
  If the line on your Toro Trimmer won't advance automatically, it could be due to several reasons. The line might be welded to itself, in which case you should lubricate it with silicone spray. Alternatively, there might not be enough line on the spool, so install more line. If the line is worn too short, pull the line while alternately pressing down on and releasing the retaining cap. The line could also be tangled; if so, remove the line from the spool and rewind it. Lastly, make sure the engine speed isn't too slow—advance the line at full throttle.
C
cassandradickersonAug 27, 2025
Why is lubricant dripping from the muffler of my Toro 51978 Trimmer?
- K
  Kathleen Rios PhDAug 27, 2025
  If lubricant is dripping from the muffler of your Toro Trimmer, ensure you are operating the product at full throttle. Also, verify that you're using fresh fuel and the correct 2-cycle lubricant mix. A dirty air filter could also be the cause, so remember to clean the air filter.
Q
qmillerSep 2, 2025
How to stop grass from wrapping around the trimmer head assembly and the attachment shaft on a Toro 51978?
- K
  Kristie RiosSep 2, 2025
  If grass wraps around the trimmer head assembly and the attachment shaft of your Toro Trimmer, avoid cutting tall grass at ground level; instead, cut from the top down. Also, ensure you are operating the product at full throttle.

Toro 51978 Specifications

General

Fuel Type	Gasoline
Engine Type	2-Cycle
Power Source	Gas
Line Diameter	0.095 inches
Line Feed	Bump
Cutting System	Dual Line

Summary

READ THIS INFORMATION

Trimmer Fueling Guide

Trimmer Engine Starting

Guidance on cold/warm starts and handling flooded engines.

Safety Information

General Trimmer Safety Rules

Comprehensive safety guidelines for operating the trimmer.

Specific Trimmer Safety Guidelines

Detailed safety guidelines specific to trimmer use.

Assembly

Trimmer Unpacking and Inspection

Attaching and Detaching Trimmer Attachments

Attaching Trimmer Front Handle

Attaching Trimmer Grass Deflector

Operation

Trimmer Fueling and Mixture Guide

Acceptable fuel types, ethanol content, and correct mix ratio.

Trimmer Fuel Tank Filling

Trimmer Starting and Stopping

Step-by-step guides for starting and stopping the engine.

How to Operate the Trimmer

How to properly use the trimmer for cutting.

Trimmer Line Advancement and Cutting Tips

Installing Trimmer Line

Maintenance

Trimmer Air Filter Cleaning

Trimmer Spark Arrestor and Plug Replacement

Trimmer Idle Speed Adjustment

Trimmer Maintenance Schedule

Schedule for routine inspection and service.

Troubleshooting

Warranty Information

Trimmer Warranty and Service

Details about product warranty, coverage, and how to get service.

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