Toro 51903; 51904; 51906; 51907 User manual

Operator’s Manual
Manuel de l’Utilisateur Manual del Usuario
FORM NO. 3319–144 REV A
16” & 18” Gas
Trimmer
Model No. 51903 — 790000001 & Up
Model No. 51904 — 790000001 & Up
Model No. 51906 — 790000001 & Up
Model No. 51907 — 790000001 & Up
16” & 18” Gas
Coupe-Herbe
Modèle No. 51903 — 790000001 et suivants
Modèle No. 51904 — 790000001 et suivants
Modèle No. 51906 — 790000001 et suivants
Modèle No. 51907 — 790000001 et suivants
16” & 18” Gas
Recortadora
Modelos N. 51903 — 790000001 y siguientes
Modelos N. 51904 — 790000001 y siguientes
Modelos N. 51906 — 790000001 y siguientes
Modelos N. 51907 — 790000001 y siguientes

The engine exhaust from this product
contains chemicals known to the State of
California to cause cancer, birth defects,
or other reproductive harm.
WARNING:
Les gaz d’échappement du moteur de ce
produit contiennent des produits
chimiques reconnus dans l’état de
Californie comme cancérigènes,
responsables de malformations
congénitales, ou comme nocifs à l’égard
des fonctions de la reproduction.
AVERTISSEMENT:
El escape del motor de esta herramienta
contiene productos químicos que según
la información del Estado de California
producen cáncer, defectos congénitos u
otros riesgos reproductivos.
ADVERTENCIA:

The Toro Company – 1996, Rev. 1997
All Rights Reserved
Printed in USA
i
Figures–Figuras
1
English
1. Model and serial number decal location
Français
1. Emplacement des numéros de modèle et de série
Español
1. Ubicación de la calcomanía con el modelo y el número de serie
1
2
3
4

ii
5
6
7
8

iii
m-2912
1
English
1. Primer bulb
Français
1. Pompe d’amorçage
Español
1. Perilla de cebado
1
234
1
5
English
1. Screw
2. Full choke position
3. Choke lever
4. Run position
5. Partial choke position
Français
1. Vis
2. Position entièrement
fermée
3. Levier du starter
4. Position de marche
5. Position partiellement
fermée
Español
1. Tornillo
2. Posición de obturación
total
3. Palanca del obturador
4. Posición de
funcionamiento
5. Posición de obturación
parcial
9
10
11

iv
1
2
English
1. Starter rope 2. Throttle trigger
Français
1. Corde du lanceur 2. Gâchette de commande
des gaz
Español
1. Cuerda de arranque 2. Gatillo del acelerador
1
English
1. Stand
Français
1. Support
Español
1. Soporte
12
13
14
15

v
16
17
18
19
20

vi
1
English
1. Air filter
Français
1. Filtre à air
Español
1. Filtro de aire
21
22
23
24
25
26

vii
1
2
3
4
English
WALBRO CARBURETOR
1. Throttle lever
2. Idle speed screw 3. High speed mixture
needle
4. Idle speed mixture needle
Français
CARBURATEUR WALBRO
1. Levier d’accélérateur
2. Vis de régime de ralenti
3. Pointeau de richesse de
haut régime
4. Pointeau de richesse de
ralenti
Español
CARBURADOR WALBRO
1. Palanca del acelerador
2. Tornillo de ajuste de la
velocidad en ralentí
3. Aguja de ajuste de la
mezcla de alta velocidad
4. Aguja de ajuste de la
mezcla de velocidad en
ralentí
27
28
29
30

viii
1
2
3
4
English
ZAMA CARBURETOR
1. Throttle lever
2. Idle speed screw 3. High speed mixture
needle
4. Idle speed mixture needle
Français
CARBURATEUR ZAMA
1. Levier d’accélérateur
2. Vis de régime de ralenti
3. Pointeau de richesse de
haut régime
4. Pointeau de richesse de
ralenti
Español
CARBURADOR ZAMA
1. Palanca del acelerador
2. Tornillo de ajuste de la
velocidad en ralentí
3. Aguja de ajuste de la
mezcla de alta velocidad
4. Aguja de ajuste de la
mezcla de velocidad en
ralentí
.020 in
(0.5 mm)
1
English
1. Muffler mounting bolts
Français
1. Boulons de montage du silencieux
Español
1. Pernos de montaje del silenciador
31 32
33

ix
1
English
1. Inlet port
Français
1. Ouverture d’entrée
Español
1. Orificio de admisión
1
English
1. Muffler gasket
Français
1. Joint du silencieux
Español
1. Junta del silenciador
34 35

EN–1
Contents
Page
Introduction 1. . . . . . . . . . . . . . . . . . . . . . . . . . . .
Safety 2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Fueling And Before Operating 2. . . . . . . . . .
While Operating 3. . . . . . . . . . . . . . . . . . . . .
Maintenance And Storage 3. . . . . . . . . . . . .
Safety and Instruction Decals 4. . . . . . . . . . .
Symbol Glossary 4. . . . . . . . . . . . . . . . . . . .
Assembly 5. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Installing The D-handle 5. . . . . . . . . . . . . . .
Installing The String Guard 5. . . . . . . . . . . .
Before Starting 5. . . . . . . . . . . . . . . . . . . . . . . . . .
Oil And Fuel 5. . . . . . . . . . . . . . . . . . . . . . .
Mixing Oil And Fuel 7. . . . . . . . . . . . . . . . .
Operation 7. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Starting/Stopping 7. . . . . . . . . . . . . . . . . . . .
Adjusting The Trimming Line Length 8. . . .
Decorative Trimming 8. . . . . . . . . . . . . . . . .
Maintenance 8. . . . . . . . . . . . . . . . . . . . . . . . . . . .
Maintenance Schedule 8. . . . . . . . . . . . . . . .
Line Installation 8. . . . . . . . . . . . . . . . . . . . .
Installing A Prewound Reel 9. . . . . . . . . . . .
Air Filter Maintenance 10. . . . . . . . . . . . . . . .
Carburetor Adjustment 10. . . . . . . . . . . . . . . .
Replacing The Spark Plug 11. . . . . . . . . . . . .
Inspecting/Cleaning The Muffler 12. . . . . . . .
Cleaning 12. . . . . . . . . . . . . . . . . . . . . . . . . . .
Storage 12. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Troubleshooting 13. . . . . . . . . . . . . . . . . . . . . . . . .
Specifications 14. . . . . . . . . . . . . . . . . . . . . . . . . . .
Engine 14. . . . . . . . . . . . . . . . . . . . . . . . . . . .
Drive Shaft & Cutting Head 14. . . . . . . . . . .
Cold Engine Torque Specifications 14. . . . . .
California Emission Control Warranty Statement 15
Warranty 17. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Introduction
Thank you for purchasing a Toro product.
All of us at Toro want you to be completely satisfied
with your new product, so feel free to contact your
local Authorized Service Dealer for help with service,
genuine Toro parts, or other information you may
require.
Whenever you contact your Authorized Service
Dealer or the factory, always know the model and
serial numbers of your product. These numbers will
help the Service Dealer or Service Representative
provide exact information about your specific
product. You will find the model and serial number
decal located in a unique place on the product
(Fig. 1).
For your convenience, write the product model and
serial numbers in the space below.
Model No.
Serial No.
Read this manual carefully to learn how to operate
and maintain your product correctly. Reading this
manual will help you and others avoid personal injury
and damage to the product. Although Toro designs,
produces and markets safe, state-of-the-art products,
you are responsible for using the product properly
and safely. You are also responsible for training
persons who you allow to use the product about safe
operation.
The Toro warning system in this manual identifies
potential hazards and has special safety messages that
help you and others avoid personal injury, even death.
DANGER, WARNING and CAUTION are signal
words used to identify the level of hazard. However,
regardless of the hazard, be extremely careful.

EN–2
DANGER signals an extreme hazard that will cause
serious injury or death if the recommended
precautions are not followed.
WARNING signals a hazard that may cause serious
injury or death if the recommended precautions are
not followed.
CAUTION signals a hazard that may cause minor or
moderate injury if the recommended precautions are
not followed.
Two other words are also used to highlight
information. “Important” calls attention to special
mechanical information and “Note” emphasizes
general information worthy of special attention.
Safety
Note: For users on U. S. Forest Land and
in the states of California, Maine,
Oregon and Washington. All U.S.
Forest Land and the state of California
(Public Resources Codes 4442 and
4443), Oregon and Washington
require, by law that certain internal
combustion engines operated on forest
brush and/or grass-covered areas be
equipped with a spark arrestor,
maintained in effective working order,
or the engine be constructed, equipped
and maintained for the prevention of
fire. Check with your state or local
authorities for regulations pertaining to
these requirements. Failure to follow
these requirements could subject you
to liability or a fine. This unit is not
factory equipped with a spark
arrestor. If these items are required in
your area, ask your dealer to install the
Optional Accessory Part #180030
Spark Arrestor Kit.
Fueling And Before Operating
1. Gasoline is extremely flammable and its vapors
can explode if ignited. Always stop the engine
and allow it to cool before filling the fuel tank.
Do not smoke while filling the fuel tank. Keep
sparks and open flames away from the area.
2. Store gasoline and fuel only in containers
designed and approved for the storage of such
materials.
3. Pressure can build up in the fuel tank. Loosen
the fuel tank cap slowly to relieve any pressure
in the tank.
4. Add fuel in a clean, well-ventilated area. Wipe
up any spilled fuel immediately. If fuel has been
spilled, allow it to dry completely before starting
the engine.
5. Move the trimmer at least 10 ft (3 m) from the
fueling point before starting the engine.
6. Thoroughly inspect the trimmer for loose or
damaged parts before each use. Do not use until
adjustments or repairs are made.
7. Avoid accidental starting. Be in the starting
position whenever pulling the starting rope.
8. Keep all bystanders, especially children, and pets
at least 33 ft (10 m) away from the area.
9. Carefully inspect the areas to be cut. Remove all
debris that could become entangled in the string
or blade. Also remove any objects that could be
thrown during cutting.
10. Before starting, make sure the string head is not
in contact with anything.
11. Always remain alert. To prevent injury to
yourself and others, do not operate this trimmer
if you are fatigued.
12. Do not operate the unit while under the influence
of drugs, alcohol or medication.

EN–3
While Operating
1. Wear safety glasses or goggles at all times when
operating this trimmer.
2. Dress properly. Do not operate this trimmer
when barefoot or wearing open sandals. Always
wear sturdy, rubber-soled footwear. The use of
gloves, ear/hearing protection and long pants are
recommended.
3. Do not wear loose fitting clothing or articles
such as scarves, strings, chains, ties, etc. because
they could get drawn into the air intake. Also
make sure long hair does not get drawn into the
air intake.
4. Keep hands, face, and feet away from all moving
parts. Do not attempt to touch or stop the string
when it is rotating.
5. Do not touch the muffler or cylinder. These parts
get extremely hot from operation and remain hot
for a short time after the equipment is turned off.
6. Always hold the trimmer with both hands when
operating. Keep a firm grip on both the front and
rear handles or grips.
7. Operate this trimmer only in a well-ventilated
area -outdoors. Carbon monoxide exhaust fumes
can be lethal in a confined area.
8. If the unit strikes or becomes entangled with a
foreign object, stop the engine immediately and
check for damage. Repair any damage before
further operation is attempted. Do not operate
the trimmer with loose or damaged parts.
9. Use the right tool. Do not use this trimmer for
any job except that for which it is intended.
10. Do not force the tool at a rate faster than the rate
at which it is able to cut effectively.
11. Do not overreach. Keep proper footing and
balance at all times.
12. Do not operate the engine faster than the speed
necessary to cut, trim or edge. Do not run the
engine at high speed when not cutting.
13. The string guard must be in place at all times
while operating the trimmer.
14. Do not extend the trimming line beyond the
length specified in this manual.
15. Always stop the engine when cutting is delayed
or when walking from one cutting location to
another.
Maintenance And Storage
1. Use only genuine Toro replacement parts when
servicing this trimmer. These parts are available
from your authorized dealer. The use of
non-standard parts, or other accessories or
attachments not approved for this trimmer, could
result in serious injury to the user or damage to
the trimmer and void your warranty.
2. Lock up and store the trimmer in an appropriate
and dry location to prevent unauthorized use and
damage. Keep unit out of the reach of children.

EN–4
Safety and Instruction Decals
Safety decals and instructions are easily visible to the operator and are located near
any area of potential danger. Replace any decal that is damaged or lost.
ON ENGINE
(Part No. 92-3332) ON BOOM
(Part No. 92-3328)
ON GAS TANK
(
Part No. 92-3334
)
Symbol Glossary
Hot surface Wear eye and hearing
protection
Stay a safe distance
from the machine
Thrown or flying
objects–Whole body
exposure
Read operator’s
manual
For service
information, call:
1–800–237–2654
Fuel Oil

EN–5
Assembly
Note: Failure to follow these assembly
instructions may cause flex shaft
failure.
Installing The D-handle
1. Push the D-handle down over the boom (Fig. 2).
2. Install the bolt, washer and wing nut and tighten
(Fig. 2).
Installing The String Guard
POTENTIAL HAZARD
•Foreign objects can be thrown by trimmer.
WHAT CAN HAPPEN
•Contact with thrown objects can cause
personal injury.
HOW TO AVOID THE HAZARD
•Never operate the trimmer without the
string guard in place.
Model 51903
1. Place the string guard onto the boom above the
clamp assembly (Fig. 3).
2. Push the string guard down to the top of the
string head assembly and then rotate the string
guard to the proper position (Fig. 4). The string
guard is in the correct position when the string
guard points toward the engine, and the holes in
the string guard line up with the holes in the top
of the string head assembly.
3. Install the screws with a Phillips screwdriver
(Fig. 5).
Model 51906
1. Slide the string guard onto the guard mount
above the string head assembly. Align the screw
holes in the string guard with the screw holes in
the string assembly (Fig. 6).
2. Place the three hex nuts into the recessed holes
on top of the guard (Fig. 7).
3. Install the screws into the holes from the bottom
of the guard. Tighten the screws (Fig. 8).
Before Starting
Oil And Fuel
THIS ENGINE IS CERTIFIED TO OPERATE
ON UNLEADED GAS AND OIL MIXTURE.
Note: BE SURE TO READ THESE
INSTRUCTIONS CAREFULLY
BEFORE ATTEMPTING TO START
OR OPERATE THIS UNIT. Using old
or improper oil or fuel, or improperly
mixing the oil and fuel can cause
engine damage. This type of damage
will void the engine warranty.

EN–6
POTENTIAL HAZARD
•In certain conditions gasoline is extremely
flammable and highly explosive.
WHAT CAN HAPPEN
•A fire or explosion from gasoline can burn
you, others, and cause property damage.
HOW TO AVOID THE HAZARD
•Use a funnel and fill the fuel tank outdoors,
in an open area, when the engine is cold.
Wipe up any gasoline that spills.
•Do not fill the fuel tank completely full.
Add gasoline to the fuel tank until the level
is 1/4” to 1/2” (6 mm to 13 mm) below the
bottom of the filler neck. This empty space
in the tank allows gasoline to expand.
•Never smoke when handling gasoline, and
stay away from an open flame or where
gasoline fumes may be ignited by a spark.
•Store gasoline in an approved container
and keep it out of the reach of children.
•Never buy more than a 30-day supply of
gasoline.
Recommended Oil Type
An 8oz. (0.24 liter) bottle of 2-cycle engine oil is
included with your product.
TORO 2-cycle oil is recommended for this outdoor
power tool. If another brand of 2-cycle oil is used,
make sure it is high quality oil, formulated for
2-cycle, air-cooled engines.
POTENTIAL HAZARD
•Gasoline/oil mixture contains petroleum
distillate.
WHAT CAN HAPPEN
•Gasoline/oil mixture can be harmful or
fatal if swallowed. It can also irritate your
skin.
HOW TO AVOID THE HAZARD
•Do not drink gasoline/oil mixture.
•Avoid prolonged contact with skin. Wash
thoroughly after handling.
•Do not reuse oil bottle.
IMPORTANT: If gasoline/oil mixture is
swallowed, do not induce vomiting. CALL
PHYSICIAN IMMEDIATELY.
Recommended Fuel Type
Use clean, fresh, unleaded gasoline that is less than
60 days old.
Note: Alcohol blended fuel absorbs moisture
(water). As little as 1% moisture in the
fuel can cause fuel and oil to separate
and form acids when stored.
If this type of fuel must be used, use
fresh fuel, (less than 60 days old) and
mix according to the mixing
instructions.
Definition Of Blended Fuels
Today’s fuels are often a blend of gasoline and one or
more oxygenates such as ethanol, methanol or MTBE
(ether).
Use Of Blended Fuels
If you choose to use a blended fuel or its use is
unavoidable, the following precautions are
recommended.

EN–7
1. Always use fresh fuel mix per your operator’s
manual.
2. Use the special additive STA-BILor an
equivalent.
3. Always agitate the fuel mix before fueling the
unit.
4. Drain the tank and run the engine dry before
storing the unit.
Use Of Fuel Additives
The use of fuel additive, such as STA-BILGas
Stabilizer or an equivalent, will inhibit corrosion and
minimize the formation of gum deposit. Add 0.8 oz
(23 ml) per gallon of fuel per instructions on
container. NEVER add fuel additives directly to the
unit’s fuel tank. Using a fuel additive can keep fuel
fresh for up to six (6) months.
Mixing Oil And Fuel
Note: For proper engine operation and
maximum reliability, pay strict
attention to the oil and fuel mixing
instructions on the 2-cycle oil
container. Use a 32:1 fuel/oil ratio
when you use 2-cycle oil. Using
improperly mixed fuel can severely
damage the engine.
Thoroughly mix the proper ratio of 2-cycle engine oil
with unleaded gasoline in a separate fuel can, 32:1.
Do not mix them directly in the engine fuel tank. See
the following table for specific gas and oil mixing
ratios.
32:1 GAS/OIL Mixing Chart
Gasoline Oil
1 US gallon 4.0 oz.
(3.8 liters) (118 ml)
1 liter 30 ml
POTENTIAL HAZARD
•Gasoline contains gasses that can build up
pressure inside a gas tank.
WHAT CAN HAPPEN
•Fuel can be sprayed on you when removing
gas cap.
HOW TO AVOID THE HAZARD
•Remove fuel cap slowly to avoid injury
from fuel spray.
Operation
Starting/Stopping
1. Mix oil with gas and fill fuel tank with fuel/oil
mixture — Per instructions on page 7.
2. Fully press and release the primer bulb 5 to 7
times. See Fig. 10 for the primer bulb location.
3. Place the choke lever in the full “choke”
position. See Fig. 11.
4. With the unit on the ground, squeeze the throttle
trigger fully and pull the starter rope briskly
(Fig. 12) until the engine sounds like it wants to
run. (Normally 2 to 5 pulls).
5. Place the choke lever in the “partial” choke
position (Fig. 11). Pull the starter rope briskly 1
to 3 times to start the engine (Fig. 12).
6. If the engine does not start, repeat steps 3
through 5.
7. After the engine warms up for 5 to 10 seconds,
place the choke lever in the “run” position
(Fig. 11).
8. To stop the engine, hold the kill switch in the
“off” position until the engine stops (Fig. 9).

EN–8
Note: When storing the unit or when setting
unit down between uses, place the unit
flat on the floor so it sits on its stand
instead of hanging it by the guard or
the cutting head (Fig. 13).
Adjusting The Trimming Line
Length
Your trimmer is equipped with a bump head that
allows the operator to release more trimming line
without stopping the engine. To release additional
line, lightly tap the trimming head on the ground
(Fig. 14 – Model 51903, Fig. 15 – Model 51906)
while operating the trimmer at high speed.
Note: Always keep the trimming line fully
extended. Line release becomes more
difficult as cutting line becomes
shorter.
Each time the head is bumped, about 1 inch
(25.4 mm) of trimming line is released. A blade in the
weed guard will cut the line to the proper length if
excess line is released.
For best results, tap the head on bare ground or hard
soil. If line release is attempted in tall grass, the
engine may stall.
Decorative Trimming
Decorative trimming is accomplished by removing all
vegetation around trees, posts, fences, etc.
(Fig. 16 – Model 51903, Fig. 17 – Model 51906).
Maintenance
Maintenance Schedule
These required maintenance procedures should be performed at the frequency stated in the table to ensure that
your unit continues to meet the 1995 California emission regulations. They should also be included as part of any
seasonal tune-up.
Frequency Maintenance Required Refer to:
Before starting engine Fill fuel tank with correct oil and fuel mixture. Page 7
Every 10 hours Clean and re-oil air filter. Page 10
Every 25 hours Inspect and clean muffler. Page 12
Every 50 hours Check spark plug condition and gap. Page 11
Line Installation
The trimming line may be replaced by two different
methods — rewinding the existing reel or installing a
prewound reel.
Rewinding The Existing Reel
To rewind the existing reel you must:
1. Check for the correct line size.
2. Remove the existing reel and spring.
3. Wind the existing reel with the new line.
4. Reinstall the existing reel and spring.

EN–9
The Correct Line To Use
POTENTIAL HAZARD
•Use of improper line could cause line to
break and be thrown in operator’s or
bystander’s direction.
WHAT CAN HAPPEN
•Use of improper line could result in serious
personal injury.
HOW TO AVOID THE HAZARD
•Use only Toroapproved replacement
monofilament line.
•Do not use any type of wire or other
string–like substance. Do not use
metal-reinforced line.
It is very important to use the correct size line. A line
with a diameter of .080 inches (2.03 mm) must be
used. The engine may overheat and fail if you use
a larger line.
Removing The Existing Reel
1. Stop engine and wait for all moving parts to
stop. Pull wire off spark plug.
2. Hold the outer spool with one hand and unscrew
the Bump Knob counterclockwise (Fig. 18).
Inspect the captured bolt inside the Bump Knob
to make sure it moves freely. Replace the Bump
Knob if it is damaged.
3. Remove the inner reel (Fig. 19).
4. Use a clean cloth to clean the inner surface of the
outer spool (Fig. 20).
Note: Always clean the inner reel, outer
spool, and shaft before reassembling
the bump head.
5. Check the indexing teeth on the inner reel and
outer spool for wear (Fig. 21). If necessary,
deburr or replace the reel and spool.
Winding The Existing Reel
1. Take approximately 25 ft (7.6 m) of new
trimming line, loop it into two equal lengths.
Insert each end of the line through one of the two
holes in the inner reel (Fig. 22). Pull the line so
that the loop is as small as possible.
2. Wind the lines, in even and tight layers, onto the
reel (Fig. 23). Wind the line in the direction
indicated on the inner reel. Be sure not to
overlap the two ends of the line.
Note: Place your index finger between the
two lines to stop the lines from
overlapping.
Note: Failure to wind the line in the direction
indicated will cause the bump head to
operate incorrectly.
3. Insert the ends of the line into the two holding
slots (Fig. 24).
Reinstalling The Reel
1. Insert the ends of the line through the eyelets in
the outer spool (Fig. 25), then grasp the ends and
pull firmly to release the line from the holding
slots in the spool.
2. Hold the inner reel in place and install the Bump
Knob in the clockwise direction (see Fig. 18).
Line installation is now complete.
Installing A Prewound Reel
1. Follow the instructions in THE CORRECT
LINE TO USE.
2. Follow the instructions in REMOVING THE
EXISTING REEL.
3. Follow the instructions in REINSTALLING
THE REEL.