Stihl SR 430, SR 450 Manual

Guide to Using this Manual

Pictograms

The meanings of the pictograms attached to or embossed on the machine are explained in this manual.
Depending on the model concerned, the following pictograms may be on your machine.

	Fuel tank for gasoline and engine oil mixture
	Press to operate manual fuel pump
	Dusting and spreading dry mode
	Flow control Mistblowing wet mode

Symbols in Text

Many operating and safety instructions are supported by illustrations.
The individual steps or procedures described in the manual may be marked in different ways:

• A bullet marks a step or procedure. A description of a step or procedure that refers directly to an illustration may contain item numbers that appear in the illustration. Example:
  • Loosen the screw (1).
  • Lever (2)

In addition to the operating instructions, this manual may contain paragraphs that require your special attention. Such paragraphs are marked with the symbols and signal words described below:

Indicates a hazardous situation that, if not avoided, will result in death or serious injury.

Indicates a hazardous situation that, if not avoided, could result in death or serious injury.
NOTICE
Indicates a risk of property damage, including damage to the machine or its individual components.

Engineering Improvements

STIHL's philosophy is to continually improve all of its products. As a result, engineering changes and improvements are made from time to time. Therefore, some changes, modifications and improvements may not be covered in this manual. If the operating characteristics or the appearance of your machine differs from those described in this manual, please contact your STIHL dealer or the STIHL distributor for your area for assistance.

Safety Precautions and Working Techniques

Because the mistblower is a power tool for spraying chemicals, special safety precautions must be observed to reduce the risk of personal injury.
It is important that you read, fully understand and observe the following general safety precautions and warnings. Read the instruction manual and the safety precautions periodically. In addition, read and follow the chemical manufacturer's instructions for the chemical products being applied. Since such products may vary greatly in handling/application requirements and risks, the product label is normally your best guide for safe and effective use.
Use your power tool for spraying chemicals and other liquids to control pests and weeds in fruit, flower and vegetable gardens, on trees and bushes and on other plants, such as coffee, tobacco and cotton. It is also useful in the maintenance of young trees for, e.g., controlling the bark beetle and other pests and plant diseases.
Only use plant protection products that are specifically approved for use in sprayers/mistblowers by their manufacturer and that meet all applicable safety regulations, standards and ordinances.

Do not use it for other purposes, since misuse may result in personal injury or property damage, including damage to the machine.
Have your STIHL dealer show you how to operate your power tool. Observe all applicable local safety regulations, standards and ordinances.
All operating and servicing personnel should be trained and familiarized with the proper handling procedures for the chemical products being used, as well as with first aid/emergency care, and liquid and dry chemical disposal regulations.

Your power tool is for professional use only. Do not lend or rent your power tool without the instruction manual. Be sure that anyone using it understands the information contained in this instruction manual.

Minors should never be allowed to use this power tool. Bystanders, especially children, and animals should not be allowed in the area where it is in use.

To reduce the risk of injury to bystanders and damage to property, never let your power tool run unattended. When it is not in use (e.g. during a work break), shut it off and make sure that unauthorized persons do not use it.
Most of these safety precautions and warnings apply to the use of all STIHL mistblowers. Different models may have different parts and controls. See the appropriate section in this instruction manual for a description of the controls and the function of the parts of your model.
Safe use of a mistblower involves

1. the operator
2. the power tool
3. the handling of the chemicals to be sprayed.
4. the use of the power tool

THE OPERATOR

Physical Condition
You must be in good physical condition and mental health and not under the influence of any substance (drugs, alcohol, etc.) which might impair vision, dexterity or judgment. Do not operate this machine when you are fatigued.

Be alert – if you get tired, take a break. Tiredness may result in loss of control. Working with any power tool can be strenuous. If you have any condition that might be aggravated by strenuous work, check with your doctor before operating this machine.

Prolonged use of a power tool (or other machines) exposing the operator to vibrations may produce whitefinger disease (Raynaud's phenomenon) or carpal tunnel syndrome.
These conditions reduce the hand's ability to feel and regulate temperature, produce numbness and burning sensations and may cause nerve and circulation damage and tissue necrosis.
All factors which contribute to whitefinger disease are not known, but cold weather, smoking and diseases or physical conditions that affect blood vessels and blood transport, as well as high vibration levels and long periods of exposure to vibration are mentioned as factors in the development of whitefinger disease. In order to reduce the risk of whitefinger disease and carpal tunnel syndrome, please note the following:
Most STIHL power tools are available with an anti-vibration ("AV") system designed to reduce the transmission of vibrations created by the machine to the operator's hands. An AV system is recommended for those persons using power tools on a regular or sustained basis.

• Wear gloves and keep your hands warm.
• Keep the AV system well maintained. A power tool with loose components or with damaged or worn AV elements will tend to have higher vibration levels.
• Maintain a firm grip at all times, but do not squeeze the handles with constant, excessive pressure. Take frequent breaks.

All the above-mentioned precautions do not guarantee that you will not sustain whitefinger disease or carpal tunnel syndrome. Therefore, continual and regular users should closely monitor the condition of their hands and fingers. If any of the above symptoms appear, seek medical advice immediately.

The ignition system of the STIHL unit produces an electromagnetic field of a very low intensity. This field may interfere with some pacemakers. To reduce the risk of serious or fatal injury, persons with a pacemaker should consult their physician and the pacemaker manufacturer before operating this tool.

Proper Clothing

To reduce the risk of injury when working with chemical agents, the operator should wear proper protective apparel when filling, using and cleaning the power tool. Always follow all of the chemical manufacturer's instructions with respect to proper eye, skin and respiratory protection. They may differ from and exceed the following precautions.

To reduce the risk of injury to your eyes never operate your power tool unless wearing goggles or properly fitted protective glasses with adequate top and side protection complying with ANSI Z87 "+".
Power tool noise may damage your hearing. Wear sound barriers (ear plugs or ear mufflers) to protect your hearing. Continual and regular users should have their hearing checked regularly.
Be particularly alert and cautious when wearing hearing protection because your ability to hear warnings (shouts, alarms, etc.) is restricted.
When working with toxic chemicals, the operator and any bystanders may need to wear a properly fitted respirator approved by NIOSH/MSHA for the chemical being used. Consult the product label. Breathing toxic chemicals can cause serious or fatal injury.

Always wear rubber/chemical-resistent gloves when handling this power tool.

For some chemicals it is advisable to wear impermeable coveralls or an impermeable work apron. Check the product label. If you are spraying overhead or if the spray may reach head height, wear a wide brim hat or other suitable head covering. Do not wear shorts, sandals or go barefoot.

Wear rubber/chemical-resistent boots.

Avoid loose-fitting jackets, scarfs, neckties, jewelry, flared or cuffed pants, unconfined long hair or anything that could become caught on branches, brush or the moving parts of the unit. Secure hair so it is above shoulder level.

In limited circumstances, mistblowers may also be used in greenhouses that are very well-ventilated if the operator can protect himself or herself from any harmful effects through the use of proper eye, skin and respiratory protection. Such work may require special precautions, and must not be prohibited on the chemical product label.

THE POWER TOOL

For illustrations and definitions of the power tool parts see the chapter on "Main Parts."

Never modify this power tool in any way. Only attachments supplied by STIHL or expressly approved by STIHL for use with the specific STIHL model are authorized. Although certain unauthorized attachments are useable with STIHL power tools, their use may, in fact, be extremely dangerous.
If this tool is subjected to unusually high loads for which it was not designed (e.g. heavy impact or a fall), always check that it is in good condition before continuing work. Check in particular that the fuel system is tight (no leaks) and that the controls and safety devices are working properly. Do not continue operating this machine if it is damaged. In case of doubt, have it checked by your STIHL servicing dealer.

Dusting and spreading mode – SR 450 only
The dusting and spreading mode can be used for powder or dry granulate up to a grain size of 5 mm.
Observe all legal requirements for handling the chemicals. Observe the directions for use on the label of the product at issue.

Using the dusting and spreading mode

An electrostatic charge may be created in the extension tube and nozzle area when applying dry materials (e.g. dusts) with the dusting and spreading attachment. This is especially true in low humidity conditions. Check the label and/or material safety data sheet for the chemical you are applying. To reduce the risk of severe or fatal injury, do not use your mistblower to apply substances that may create a combustible or explosive dust cloud. For instance, never use your mistblower to apply sulfur or sulfur compounds, since they may be highly explosive and have relatively low melting and ignition points.

To reduce the risk of sparking when applying any dry substance, make sure that the discharge system (antistatic wire in the mistblower connected to a metal chain) is completely and properly mounted to the machine, and that the discharge chain is making contact with the ground. It is essential to follow the assembly instructions – see the chapter "Assembling the Unit" in this instruction manual.
Do not use the dusting and spreading attachment on non-conductive surfaces (e.g. plastic, asphalt).
Never operate your machine with a missing or damaged discharge system.

HANDLING OF CHEMICALS

Some chemicals sprayed with your power tool may contain toxic and/or caustic substances. Such chemicals can be dangerous and cause serious or fatal injury to persons and animals and/or severe damage to plants and the environment.
Avoid direct contact with chemicals. Follow the chemical manufacturer's instructions with respect to any contact with its product.

Read the label each time before mixing or using the chemical and before storing or disposing of it. Do not trust your memory. Careless or improper use may cause serious or fatal injury.

Chemicals can be harmful to individuals, animals and the environment if improperly used. In addition, some chemicals that are caustic, corrosive or poisonous should not be used in your mistblowers.
Carefully read the labels on chemical containers prior to use. Chemicals are classified into categories of toxicity. Pesticides regulated by the EPA, for instance, use signal words to indicate the product's potential to make you sick. "Caution" appears on pesticides found to be least harmful to humans. "Warning" indicates a product that is more poisonous than those in the "Caution" group. Pesticides with the signal word "Danger" on the label are very poisonous or irritating. They should be used with extreme care. Finally, pesticides labeled "Danger – Poison" are for restricted use only and generally must be used under the supervision of a certified applicator. Each category will have unique handling characteristics. Familiarize yourself with the characteristics for the category you are using.
Chemicals may be used only by persons trained in their handling and the appropriate first-aid measures.

Mix only compatible pesticides. Wrong mixtures can produce toxic fumes.
When handling chemicals and when spraying, make sure you are operating in accordance with local, state, and federal environmental protection rules and guidelines. Do not spray in windy conditions. To help protect the environment, use only the recommended dosage – do not overuse. Pay special attention when using near watersheds, waterway, etc.

Do not eat, drink, or smoke while handling chemicals or while you are spraying. Never blow through nozzles, valves, pipes or any other component by mouth. Always handle chemicals in a well-ventilated area while wearing appropriate protective clothing and safety equipment. Do not store or transport chemicals together with food or medicines, and never reuse a chemical container for any other purpose.
Do not transfer dry or liquid chemicals to other containers, especially food and/or drink containers.

In case of accidental contact or ingestion of chemicals or in case of contamination of clothing, stop work and immediately consult the chemical manufacturer's instructions. If in doubt as to what to do, consult a poison control center or doctor without delay. Have the product's label available to read to or show the persons you consult.
Clean all chemical spills immediately. Dispose of any residue in accordance with state or federal laws and regulations.

Keep chemicals out of reach of children, other unauthorized people and animals. When not in use, store chemicals in a safe place. Follow the manufacturer's recommendations for proper storage.

Preparing chemicals
Prepare chemical solutions of according to manufacturer's instructions.

• Only prepare sufficient solution for the job at hand so that nothing is left over.
• Mix chemicals only in accordance with instructions – wrong mixtures can produce toxic fumes or explosive mixtures.
• Never spray chemicals undiluted.
• Prepare solution and fill the container outdoors only, in wellventilated locations.

Storage

• Do not store spray solution in the container for longer than one day.
• Store and transport spray solution only in approved containers.
• Never store the spray solution in containers intended for foods, drinks or animal feed.
• Do not store spray solution with foods, drinks or animal feed.
• Keep spray solution out of the reach of children and animals.
• Store the spray solution in a place secured against unauthorized use.

THE USE OF THE POWER TOOL

Transporting the Power Tool

Always switch off the engine before taking the machine off your back and putting it down. Empty container when transporting it in a vehicle; properly secure it to prevent turnover, fuel spillage and damage to the unit.

Fuel
Your STIHL power tool uses an oil- gasoline mixture for fuel (see the chapter on "Fuel" in this instruction manual).

Gasoline is an extremely flammable fuel. If spilled and ignited by a spark or other ignition source, it can cause fire and serious burn injury or property damage. Use extreme caution when handling gasoline or fuel mix. Do not smoke or bring any fire or flame near the fuel or the power tool. Note that combustible fuel vapor may escape from the fuel system.

Fueling Instructions

To reduce the risk of serious injury from burns, never attempt to refuel the unit until it has been completely removed from the operator.

Fuel your power tool in well-ventilated areas, outdoors. Always shut off the engine and allow it to cool before refueling. Gasoline vapor pressure may build up inside the fuel tank depending on the fuel used, the weather conditions and the tank venting system.
In order to reduce the risk of burns and other personal injury from escaping gas vapor and fumes, remove the fuel filler cap on your power tool carefully so as to allow any pressure build-up in the tank to release slowly. Never remove the fuel filler cap while the engine is running.
Select bare ground for fueling and move at least 10 feet (3 m) from the fueling spot before starting the engine. Wipe off any spilled fuel before starting your machine.

Check for fuel leakage while refueling and during operation. If fuel leakage is found, do not start or run the engine until the leak is fixed and any spilled fuel has been wiped away. Take care not to get fuel on your clothing. If this happens, change your clothing immediately.

In order to reduce the risk of fuel spillage and fire from an improperly tightened fuel cap, correctly position and tighten the fuel cap in the fuel tank opening.
Different models may be equipped with different fuel caps.
See also the "Fueling" chapter in your Instruction Manual for additional information.

Bayonet Fuel Filler Cap

Never use a tool to open or close the bayonet fuel filler cap, as this could damage the cap and cause fuel to leak out.
The bayonet fuel filler cap must be closed with care after refuelling.

Screw Cap


Unit vibrations can cause an improperly tightened fuel filler cap to loosen or come off and spill quantities of fuel. In order to reduce the risk of fuel spillage and fire, tighten the fuel filler cap by hand as securely as possible.

Filling the Container

Tighten all connections and check to be sure the hose is securely attached and in good condition. Keep the valve lever on the control lever closed.
Before using the power tool with chemicals, fill it with fresh water to assure that you have it properly assembled and practice spraying. Also, check for any leaks at this time. When thoroughly familiar with the power tool operation, follow normal operating procedures.
Fill your power tool in well-ventilated areas, outdoors.

Do not use:

• flammables in the mistblower, which can explode causing serious or fatal injury;
• caustic or corrosive materials in the mistblower, that could result in damage to the unit;
• liquids with a temperature above 120°F (50°C) to avoid scalding and damage to the unit.

To fill the container, place the power tool on a level surface. To reduce the risk of contaminating the surrounding environment, be careful not to overfill the container with chemical solution.
To reduce the risk of injury, do not fill the unit while wearing it on your back.
If you fill the container with a hose attached to a central water supply, be sure the end of the hose is out of the solution to reduce the risk of backflow, i.e. the chemicals being sucked into the water supply in the case of a sudden vacuum.
Calculate the correct amount of chemical solution so that it is used up at one time, with no extra solution left in the tank.
After filling, fit the container cap and tighten it down firmly.

Check for leakage while refilling and during operation. A leak from the container or a loose fitting could soak your clothing and come into contact with your skin.

Before Starting

Always check your power tool for proper condition and operation before starting, particularly the throttle trigger and setting lever with stop position. The throttle trigger must move freely and always spring back to the idle position. Never attempt to modify the controls or safety devices.

Check fuel system for leaks, especially the visible parts, e.g., filler cap, hose connections, manual fuel pump (only for power tools equipped with a manual fuel pump). Do not start the engine if there are leaks or damage – risk of fire! Have the machine repaired by a servicing dealer before using it.

To reduce the risk of leakage and skin contact with chemicals, check that the container cap and all connections in the path of the spray are tight, and be sure the hose is securely attached and in good condition. Keep the valve lever closed.

Never operate your power tool if it is damaged, improperly adjusted or maintained, or not completely or securely assembled.

Check that the spark plug boot is securely mounted on the spark plug – a loose boot may cause arcing that could ignite combustible fumes and cause a fire.
Keep the control handle clean and dry at all times; it is particularly important to keep it free of moisture, pitch, oil, fuel mix, grease or resin in order for you to maintain a firm grip and properly control your power tool.

To reduce the risk of injury from thrown parts, check the fan housing for damage (cracks, nicks, chipping). If any damage is found, stop using the unit and contact your STIHL dealer for repair.
Check condition of harness straps and replace damaged or worn straps.

Adjust carrying harness to suit your size before starting work.

In an emergency, you may slip out of the harness and throw off the machine quickly. Try slipping out of the harness a number of times before using the machine in order to become accustomed to it. Do not throw off the machine while practicing as it could damage the machine.

Starting
Start the engine at least 10 feet (3 m) from the fueling spot, outdoors only.

Your power tool is a one-person machine. To reduce the risk of eye or other injury from thrown objects, insure that bystanders are at least 50 feet (15 m) away when starting and during use. Stop operation immediately if you are approached.
For specific starting instructions, see the appropriate section in this instruction manual. Place the power tool on firm ground or other solid surface in an open area. Maintain good balance and secure footing.

When you pull the starter grip, do not wrap the starter rope around your hand. Do not let the grip snap back, but guide the starter rope to rewind it properly. Failure to follow this procedure may result in injury to your hand or fingers and may damage the starter mechanism.
The assistance of another person may be needed in placing the unit on your back after starting. In order to reduce the risk of injury to the assistant from thrown objects, chemical spray/dust or from contact with hot exhaust fumes, the engine should be kept at idle speed during this brief period, and your assistant should not stand in the area of the outlet nozzle or exhaust. Otherwise, the unit should be started and operated without assistance.

During Operation
Holding and Controlling the Power Tool

The mistblower is designed for singlehanded operation with the right hand on the control handle. It should be carried as a backpack with the straps of the harness over both shoulders.

To reduce the risk of loss of control, never carry the unit with the strap(s) over one shoulder.
Wrap your fingers tightly around the handle, keeping the control handle cradled between your thumb and forefinger. Keep your hand in this position to have your machine under control at all times.

In order to keep the container upright and reduce the risk of spillage, do not bend at the waist. Bend only at the knees and support yourself as required to ensure proper balance.
Remember that a mistblower filled with liquid has a significant amount of weight. Use caution when bending, leaning or walking.

Do not overreach. Keep proper footing and balance at all times. Special care must be taken in slippery conditions (wet ground, snow and ice) and in difficult, overgrown terrain. Watch for hidden obstacles such as tree stumps, roots and ditches to avoid stumbling. For better footing, clear away fallen branches, scrub and cuttings. Be extremely cautious when working on slopes or uneven ground.
To reduce the risk of stumbling and loss of control, do not walk backward while operating the machine. Avoid stepping on antistatic chain – SR 450 only.

To reduce the risk of injury from loss of control, never work on a ladder, in a tree or on any other insecure support.
During work breaks, do not leave the power tool in the hot sun or near any heat source.

Working Conditions
Operate and start your power tool only outdoors in a well-ventilated area. Operate it under good visibility and daylight conditions only. Work carefully.

As soon as the engine is running, this product generates toxic exhaust fumes containing chemicals, such as unburned hydrocarbons (including benzene) and carbon monoxide, that are known to cause respiratory illness/injury, cancer, birth defects, or other reproductive harm. Some of the gases (e.g. carbon monoxide) may be colorless and odorless. To reduce the risk of serious or fatal injury/illness from inhaling toxic fumes, never run the machine indoors or in poorly ventilated locations.

Inhalation of chemicals can cause susceptible persons to have an allergic or asthmatic reaction.
Substantial or repeated inhalation of certain chemicals may cause respiratory disease, cancer, birth defects or other reproductive harm. Control the chemical spray/dust at the source where possible. Use good work practices, such as operating the unit so that the wind or operating process does not blow the chemical spray/dust back on the operator. Follow the recommendations of EPA/OSHA/NIOSH and occupational and trade associations with respect to proper usage. When the inhalation of the chemical spray/dust being applied cannot be avoided, the operator and any bystanders may need to wear a respirator approved by NIOSH/MSHA for the type of chemical encountered. Consult the label of the chemical product being used.

If you are unfamiliar with the risks associated with the particular chemical at issue, review the product label and/or material safety data sheet for that substance and/or consult the material manufacturer/supplier. You may also consult your employer, governmental agencies such as the EPA, OSHA and NIOSH and other sources on hazardous materials. The state of California and some other authorities, for instance, have published lists of substances known to cause cancer, reproductive toxicity, etc.

Operating instructions

In the event of an emergency, switch off the engine immediately – move the setting lever to 0 or STOP.

Never spray in the direction of humans, animals or property which might be injured or damaged by spray formula.
Pay attention to the direction of the wind, i.e., do not work against the wind. When spraying, stand so that the wind does not blow towards you or bystanders.
Keep children and pets away from areas that have just been sprayed. After the use of some chemicals, especially agricultural pesticides, a notice must be posted on the treated area that a "Restricted Entry Interval" (REI) is in effect. See the product's label and any applicable governmental regulations.

Your power tool is not insulated against electric shock. To reduce the risk of electrocution, never operate this power tool in the vicinity of any wires or cables (power, etc.) which may be carrying electric current. Do not spray on or near electrical installations.

To reduce the risk of personal injury, do not direct air blast towards bystanders, since the high pressure of the air flow could injure eyes and could blow small objects at great speed.

The blower fan between the air intake and output openings rotates whenever the engine is running.
Never insert any foreign object into the air intake of the machine or into the nozzle of the blower. It will damage the fan wheel and may cause serious injury to the operator or bystanders as a result of the object or broken parts being thrown out at high speed.
Do not place the blower on the ground when operating at high speed, because small objects such as sand, grass, dust, etc. may be pulled into the air intake and damage the fan wheel.

Never modify your muffler. Any modification could cause an increase in heat radiation, sparks or sound level, thereby increasing the risk of fire, burn injury or hearing loss. You may also permanently damage the engine. Have your muffler serviced and repaired by your STIHL servicing dealer only.

The muffler and other parts of the engine (e.g. fins of the cylinder, spark plug) become hot during operation and remain hot for a while after stopping the engine. To reduce risk of burns, do not touch the muffler and other parts while they are hot. Keep the area around the muffler clean. Remove excess lubricant and all debris such as pine needles, branches or leaves. Let the engine cool down sitting on concrete, metal, bare ground or solid wood away from any combustible substances.

An improperly mounted or damaged cylinder housing or a damaged/deformed muffler shell may interfere with the cooling process of the muffler. To reduce the risk of fire or burn injury, do not continue work with a damaged or improperly mounted cylinder housing or a damaged/deformed muffler shell.
Your muffler is furnished with a spark arresting screen designed to reduce the risk of fire from the emission of hot particles. Never operate your unit with a missing or damaged spark arresting screen. If your gas/oil mix ratio is correct (i.e., not too rich), this screen will normally stay clean as a result of the heat from the muffler and need no service or maintenance. If you experience loss of performance and you suspect a clogged screen, have your muffler maintained by a STIHL servicing dealer. Some state or federal laws or regulations may require a properly maintained spark arrestor for certain uses. See the "Maintenance, Repair and Storing" section of these Safety Precautions. Remember that the risk of a brush or forest fire is greater in hot or dry conditions.

Some STIHL power tools are equipped with a catalytic converter, which is designed to reduce the exhaust emissions of the engine by a chemical process in the muffler. Due to this process, the muffler does not cool down as rapidly as conventional mufflers when the engine returns to idle or is shut off. To reduce the risk of fire and burn injuries when using a catalytic converter, always set your power tool down in the upright position and never locate it where the muffler is near dry brush, grass, wood chips or other combustible materials while it is still hot.

After Finishing Work
Always wash yourself thoroughly with soap and water after spraying or handling chemicals. Shower immediately, and wash all protective clothing separately from other items. Follow any additional recommendations of the chemical manufacturer.
Always clean dust and dirt off the power tool.

Empty, rinse and clean container and assembly after each use. This helps to prevent the solution from crystallizing, which could later cause clogging and chemical damage to the unit. In addition, residual chemicals may have undesirable effects during subsequent spraying with a different type of chemical (e.g., residual herbicide may damage or kill plants being sprayed with a pesticide).
Do not store the mistblower with spray solution in the container.
Store the unit in a place secured against unauthorized use.

MAINTENANCE, REPAIR AND STORING

Maintenance, replacement, or repair of the emission control devices and systems may be performed by any nonroad engine repair establishment or individual. However, if you make a warranty claim for a component which has not been serviced or maintained properly or if nonapproved replacement parts were used, STIHL may deny coverage.

Use only identical STIHL replacement parts for maintenance and repair. Use of non-STIHL parts may cause serious or fatal injury.
Strictly follow the maintenance and repair instructions in the appropriate section in this instruction manual. Please refer to the maintenance chart in this instruction manual.

Always stop the engine and make sure that the fan is stopped before doing any maintenance or repair work or cleaning the power tool. Do not attempt any maintenance or repair work not described in this instruction manual. Have such work performed by your STIHL servicing dealer only.
Do not clean your machine with a pressure washer. The solid jet of water may damage parts of the machine.

Use the specified spark plug and make sure it and the ignition lead are always clean and in good condition. Always press spark plug boot snugly onto spark plug terminal of the proper size. (Note: If terminal has detachable SAE adapter nut, it must be securely attached.) A loose connection between spark plug terminal and the ignition wire connector in the boot may create arcing that could ignite combustible fumes and cause a fire.

Never test the ignition system with the boot removed from the spark plug or with a removed spark plug, since uncontained sparking may cause a fire.

Do not operate your power tool if the muffler is damaged, missing or modified. An improperly maintained muffler will increase the risk of fire and hearing loss. Your muffler is equipped with a sparkarresting screen to reduce the risk of fire; never operate your power tool if the screen is missing, damaged or clogged. Remember that the risk of a brush or forest fire is greater in hot or dry weather.
In California, it is a violation of § 4442 or § 4443 of the Public Resources Code to use or operate gasoline-powered tools on forest-covered, brush-covered or grass-covered land unless the engine's exhaust system is equipped with a complying spark arrester that is maintained in effective working order. The owner/operator of this product is responsible for properly maintaining the spark arrester. Other states or governmental entities/agencies, such as the U.S. Forest Service, may have similar requirements. Contact your local fire agency or forest service for the laws or regulations relating to fire protection requirements.
Tighten all nuts, bolts and screws except the carburetor adjustment screws after each use.
For maintenance items please also refer to the maintenance chart in this instruction manual.
Store the power tool in a dry and high or locked location out of reach of children.
Before storing for longer than a few days, always empty the fuel tank. See chapter "Storing the machine" in this instruction manual.
Store fuel in an approved and properly labeled safety-type canister only. Take care when handling gasoline! For health and safety reasons, avoid direct contact with the skin and avoid inhaling fuel vapor!

Assembling the Unit

NOTICE
Hose and throttle cable, and the metering unit's operating cable on the SR 450, come connected ready for use and must not be kinked while assembling the machine.
The combination wrench and screwdriver are in the supplied accessory bag.

Fitting the pleated hose on the blower tube

• Push wide hose clamp (1), marks facing right, onto the blower tube (2).
  
• Push the ring seal (3) (wide lip facing left) onto the stub on the blower tube (2).
  
• Push the pleated hose (4) over the ring seal (3).
• Push the hose clamp (1) onto the pleated hose (4).
  
• Line up the marks on the hose clamp (1) and blower tube (2) – as shown.
• Secure the hose clamp (1) with the screw (5) – the blower tube (2) must still rotate.

Fitting the pleated hose on the elbow

SR 430 only

• Push narrow hose clamp (1), marks facing left, onto the elbow (2).
• Push the pleated hose (3) onto the elbow (2).
• Push the hose clamp (1) onto the pleated hose (3).
  
• Line up the marks on the hose clamp (1) and elbow (2) – as shown.
• Secure the hose clamp (1) with the screw (4).

Fitting the antistatic system

SR 450 only

• Attach the antistatic wire (1) and chain (2) to the blower housing with screw (3).

Fitting the pleated hose on the elbow

SR 450 only

• Push the antistatic wire (1) into the pleated hose (2).
• Push narrow hose clamp (3), marks facing left, onto the elbow (4).
  
• Route the antistatic wire (1) through the slot in the hose clamp (3).
• Push the pleated hose (2) onto the elbow (4).
• Push the hose clamp (3) onto the pleated hose (2).
  
• Line up the marks on the hose clamp (3) and elbow (4) – as shown.
• Secure the hose clamp (3) with the screw (5) – make sure the antistatic wire is located in the notch.

Adjusting and securing the control handle

• Put the machine on your back and adjust the harness – see "Harness".
• Slide the control handle (1) along the tube to the most comfortable position – distance between nozzle outlet (2) and the control handle (1) must be at least 19.7 in (500 mm) ('a').
  
• Secure the control handle (1) with the screw (3).
  
• Use the retainer (4) to secure the hose and throttle cable, and metering unit's operating cable on the SR 450, to the 6th pleat (arrow) on the pleated hose.
  

Adjusting the Throttle Cable

It may be necessary to correct the adjustment of the throttle cable after assembling the machine or after a prolonged period of operation.
Adjust the throttle cable only when the unit is completely and properly assembled.

• Set throttle trigger to the full throttle position – as far as stop.
• Carefully rotate the screw in the throttle trigger in the direction of the arrow until you feel initial resistance. Then rotate it another full turn.

Harness

Adjusting the Harness

• Pull the ends of the straps downwards to tighten the harness.
• Adjust the harness so that the backplate fits snugly and securely against your back.

Loosening the Harness

• Lift the tabs of the sliding adjusters.

Fuel

This engine is certified to operate on unleaded gasoline and the STIHL twostroke engine oil at a mix ratio of 50:1.
Your engine requires a mixture of highquality gasoline and two-stroke air cooled engine oil.
Use mid-grade unleaded gasoline with a minimum octane rating of 89 ((R+M)/2) and no more than 10% ethanol content.
NOTICE
Fuel with an octane rating below 89 may increase engine temperatures. This, in turn, increases the risk of piston seizure and damage to the engine.
The chemical composition of the fuel is also important. Some fuel additives not only detrimentally affect elastomers (carburetor diaphragms, oil seals, fuel lines, etc.), but magnesium castings and catalytic converters as well. This could cause running problems or damage the engine. For this reason STIHL recommends that you use only quality unleaded gasoline!
NOTICE
Gasoline with an ethanol content of more than 10% can cause running problems and major damage in engines and should not be used.
For further details, see www.STIHLusa.com/ethanol
The ethanol content in gasoline affects engine speed – it may be necessary to readjust the carburetor if you use fuels with various ethanol contents.

To reduce the risk of personal injury from loss of control and/or contact with the running cutting tool, do not use your unit with an incorrect idle adjustment. At correct idle speed, the cutting tool should not move.
If your machine's idle speed is incorrectly adjusted, have your authorized STIHL servicing dealer check your machine and make the proper adjustments and repairs.
The idle speed and maximum speed of the engine change if you switch from a fuel with a certain ethanol content to a fuel with a much higher or lower ethanol content.
This problem can be avoided by always using fuel with the same ethanol content.
To ensure the maximum performance of your STIHL engine, use a high quality 2cycle engine oil. To help your engine run cleaner and reduce harmful carbon deposits, STIHL recommends using STIHL HP Ultra 2-cycle engine oil or ask your dealer for an equivalent fully synthetic 2-cycle engine oil.
To meet the requirements of EPA and CARB we recommend to use STIHL HP Ultra oil.

STIHL MotoMix

STIHL recommends the use of STIHL MotoMix. STIHL MotoMix has a high octane rating and ensures that you always use the right gasoline/oil mix ratio.
STIHL MotoMix uses STIHL HP Ultra two-stroke engine oil suited for high performance engines.
For further details, see www.STIHLusa.com/ethanol
If not using MotoMix, use only STIHL two-stroke engine oil or equivalent highquality two-stroke engine oils that are designed for use in air cooled two-cycle engines.
The use of non-seasonal gasoline blends may increase the potential for pressure to build in the fuel tank during operation. For example, using a winder blend during the summer will increase pressure in the fuel tank. Always use gasoline blends appropriate to the season, altitude and other environmental factors.
Do not use BIA or TCW rated (twostroke water cooled) mix oils or other mix oils that state they are for use in both water cooled and air cooled engines (e.g., outboard motors, snowmobiles, chain saws, mopeds, etc.).

Take care when handling gasoline. Avoid direct contact with the skin and avoid inhaling fuel vapor. When filling at the pump, first remove the container from your vehicle and place the container on the ground before filling. To reduce the risk of sparks from static discharge and resulting fire and/or explosion, do not fill fuel containers that are sitting in or on a vehicle or trailer.
The container should be kept tightly closed in order to limit the amount of moisture that gets into the mixture.
The machine's fuel tank should be cleaned as necessary.

Fuel mix ages

If not using MotoMix, only mix sufficient fuel for a few days of work, not to exceed 30 days of storage. Store in approved fuel-containers only. When mixing, pour oil into the container first, and then add gasoline. Close the container and shake it vigorously by hand to ensure proper mix of oil and gasoline.

Dispose of empty mixing-oil containers only at authorized disposal locations.

Fueling

Preparations

• Before fueling, clean the fuel filler cap and the area around it so that dirt cannot fall into the tank.

Thoroughly shake up the mixture in the canister before fueling your machine.

In order to reduce the risk of fire and personal injury from escaping gas vapor and fumes, remove the fuel filler cap carefully so as to allow any pressure build-up in the tank to release slowly.
Do not spill any fuel and do not fill the tank up to the brim.
Your power tool comes standard with either a screw-type or bayonet-type fuel cap.

Bayonet fuel cap

Screw-type tank cap

Open the bayonet fuel filler cap

Never use a tool to open the bayonet catch. This could damage the cap and cause fuel to leak out.

• Press the cap down with your hand as far as possible, turn it counterclockwise (approx. 1/8 turn) and remove it.

Fueling
Take care not to spill fuel while fueling and do not overfill the tank.

Close the bayonet fuel filler cap

• Fit the cap and turn it until it engages in the bayonet mount.
• Press the cap down with your hand as far as possible and turn it clockwise (approx. 1/8 turn) until it engages completely.

Opening the threaded filler cap

• Turn the cap counterclockwise until it can be removed from the tank opening.
• Remove the filler cap.

Refueling
Take care not to spill fuel while fueling and do not overfill the tank.

Closing the threaded filler cap

• Position cap.
• Turn the cap clockwise as far as it will go and tighten it as securely as possible by hand.

Information Before You Start

NOTICE
With the engine stopped and before starting, check the air intakes between the backplate and powerhead for blockages and clean if necessary.

Control handle

1. Setting lever
2. Throttle trigger
3. Throttle trigger lockout

Functions of setting lever

Run position I
Engine runs or is ready to start. Throttle trigger (2) can be moved to any position.

Stop position 0
Ignition is interrupted, engine stops. The setting lever (1) is not locked in this position. It springs back to the run position. The ignition is switched on again.

Throttle trigger limiter position
Travel of throttle trigger can be limited in two stages:

1. 1/3 throttle
2. 2/3 throttle

To disengage the travel limiter,

• return the setting lever (1) to the run position I.

Starting/Stopping the Engine

Before Starting

• Close valve lever (1) for solution feed.

Additionally on SR 450:

• Close the metering lever (2) for dusting and spreading mode.

Starting the Engine

• Observe safety precautions.

NOTICE
Start your unit on a clean, dust-free surface only to ensure that no dust is sucked in.

• The setting lever must be on I
  
• Press the manual fuel pump bulb (3) at least five times – even if the bulb is filled with fuel.
  

Cold engine (cold start)

• Press in the choke knob (4) and turn it to .

Warm engine (warm start)

• Press in the choke knob (4) and turn it to .

Also use this setting if the engine has been running but is still cold.

Cranking

• Place the unit securely on the ground and make sure that bystanders are well clear of the nozzle outlet.
• Make sure you have a firm footing: Hold the unit with your left hand on the housing and put one foot against the base plate to prevent it slipping.
• Pull the starter grip slowly with your right hand until you feel it engage and then give it a brisk strong pull. Do not pull out the starter rope to full length – it might otherwise break.
• Do not let the starter grip snap back. Guide it slowly back into the housing so that the starter rope can rewind properly.
• Continue cranking until the engine runs.

As soon as the engine runs

• Pull the throttle trigger – the choke knob (4) automatically returns to the run position ().

At very low outside temperatures

• Open throttle slightly – warm up the engine for a short period.

Stopping the Engine

• Move the setting lever in the direction of 0 – the engine stops – the setting lever springs back to the on position.
  

Other Hints on Starting

Engine stalls in cold start position or under acceleration

• Move the choke knob to and continue cranking until the engine runs.

Engine does not start in warm start position

• Move the choke knob to and continue cranking until the engine runs.

If the engine does not start

• Check that all settings are correct.
• Check that there is fuel in the tank and refuel if necessary.
• Check that the spark plug boot is properly connected.
• Repeat the starting procedure.

Fuel tank run until completely dry

• After refueling, press the manual fuel pump bulb at least five times – even if the bulb is filled with fuel.
• Set the choke knob according to engine temperature.
• Now start the engine.

Operating Instructions

During Operation
After a long period of full throttle operation, allow the engine to run for a short while at idle speed so that engine heat can be dissipated by the flow of cooling air. This helps protect enginemounted components (ignition, carburetor) from thermal overload.

After Finishing Work
Storing for a short period: Wait for the engine to cool down. Keep the machine in a dry place, well away from sources of ignition, until you need it again. For longer out-of-service periods – see "Storing the Machine".

Calculating Required Quantity of Solution

Determining surface area (m²)

In the case of ground crops, simply multiply the length of the field by its width.
The surface area of high-growing plants is calculated approximately by measuring the length of the rows and the average height of the foliage. The result is multiplied by the number of rows and then by two if both sides have to be treated.
The surface area in hectares is obtained by dividing the number of square meters by 10,000.
Example:
A field 120 meters long and 30 meters wide has to be treated with a pesticide.
Area:
120 m x 30 m = 3,600 m²
3,600/10,000 = 0.36 ha

Determining quantity of active ingredient

Refer to the instructions supplied with the active ingredient to determine:

• Required quantity of active ingredient for 1 hectare (ha).
• Concentration of active ingredient (mix ratio).

Multiply the required quantity of active ingredient for 1 hectare by the area determined in hectares. The result is the quantity of active ingredient required for the area to be treated.
Example:
According to the maker's instructions, 0.4 liters of active ingredient are required per hectare to obtain a concentration of 0.1%.
Quantity of active ingredient:
0.4 (l/ha) x 0.36 (ha) = 0.144 l

Determining quantity of solution

The quantity of solution required is calculated as follows:

T_W = Quantity of active ingredient in l
K = Concentration in %
T_B = Required quantity of solution in l
Example:
The calculated quantity of active ingredient is 0.144 liters. According to the maker's instructions, the concentration is 0.1%.
Quantity of solution:

Determining walking speed

Carry out a trial run with the machine fueled and the container filled with water. Operate the spray tube (swing it back and forth) as for the real run described below. Determine the distance walked in one minute.
Also use the trial run to check the selected working width. The best working width for low-growing crops is 4–5 m. Mark the working width with stakes.
Dividing the distance walked in meters by the time in minutes gives you the walking speed in meters per minute (m/min).
Example:
The distance covered in one minute is 10 meters.
Walking speed:

Determining discharge rate

The setting of the metering unit is calculated as follows:

V_a = Quantity of solution
V_b = Walking speed
V_c = Discharge rate b = Working width
A = Area
Example:
The values determined above and a working width of 4 meters require the following setting on the metering unit:

Hectares (ha) have to be converted into m² (ha x 10,000 = m²).
To adjust the required discharge rate see "Metering Unit".

Metering Unit

Valve lever

Solution feed is started and stopped with the valve lever (1).

• Position A (valve lever vertical, up) – open
• Position B (valve lever horizontal, down) – closed

Metering knobs

The scope of supply includes metering knobs which allow a wide range of different discharge rates.

• Standard metering knob (A) with positions 1 to 6
• Pressure pump' metering knob¹⁾ (B) with positions 1 to 2.3
• ULV metering knob¹⁾ (C) with positions 0.5 to 0.8

Changing the metering knob

• Pull the existing metering knob up and out of its seat.
• Push the new metering knob into its seat as far as stop.

Fitting the strainer ²⁾

The strainer supplied must always be fitted when the ULV metering knob is used.

• Push the strainer into its seat until it snaps into position.

Removing

• Pry the strainer out of its seat – as shown.

1. Standard equipment or available as special accessory
2. Included with ULV metering knob

Adjusting the discharge rate

• Rotate the metering knob (1) for infinitely variable discharge rate
  

Position 1 = minimum flow rate
Position 6 = maximum flow rate
The numbers on the metering knob must be lined up with the lug (2) under the knob.
The "E" position on the ULV metering knob is used for emptying the solution container. Do not use this position for spraying – see "After Finishing Work".

Machines with pressure pump (special accessory)
On machines with pressure pump, use only the 'pressure pump' metering knob or the ULV metering knob.

Discharge rate

Discharge rate (l/min) without pressure pump, with standard metering knob:

Discharge rate (l/min) without pressure pump, with ULV nozzle

Discharge rate (oz/min) without pressure pump, with standard metering knob:

Discharge rate (oz/min) without pressure pump, with ULV nozzle

Discharge rate with pressure pump, with 'pressure pump' metering knob:
Spray tube angle -30° to +30°

Discharge rate with pressure pump, with ULV nozzle

Checking flow rate

• Place the unit on the ground.
• Fill the container with water up to 10 liter mark.

Machines without pressure pump

• Set the standard metering knob to 6.
• Start the machine.
• Hold the spray tube horizontally, run the engine at full throttle, spray the contents of the container down to the 5 liter mark and note the time taken.

The time required to spray 5 liters fluid should be between 75 and 105 seconds.

Machines with pressure pump

• Set the 'pressure pump' metering knob to 2.3.
• Start the machine.
• Hold the spray tube horizontally, run the engine at full throttle, spray the contents of the container down to the 5 liter mark and note the time taken.

The time required to spray 5 liters fluid should be between 60 and 90 seconds.

In case of deviations:

• Check the container, hose system, metering knob and optional pressure pump for contamination and clean if necessary.
• Check blower air intake and clean if necessary.
• Check engine setting and correct if necessary.

If there is no improvement, contact your dealer for assistance.

Dusting and Spreading Mode

SR 450 only.

Metering lever

The discharge rate is infinitely variable with the metering lever (1).

• Position A (metering lever vertical) – feed closed
• Position B (metering level parallel to blower tube) – feed open

Discharge rates

The discharge rate is dependent on the density and grain size of the product used.

Conversion from mistblowing to dusting and spreading mode

• Empty and clean the solution container – see "After Finishing Work".
• Close the valve lever (1) for solution feed.
  
• Close the metering lever (2) for dusting and spreading mode.
  

Solution container
The selected operating mode is indicated by the symbols on the metering unit's housing.

• Position A – Mistblowing mode
• Position B – Dusting and spreading mode
• Insert a suitable tool (e.g. screwdriver) in the two recesses (arrows) to loosen the strainer (1).
  
• Pull the strainer (1) upward and out of the solution container.
• Squeeze the tabs (2) together and pull the lever (3) outwards.
  
• Remove the solution container from the metering unit's housing (4) and turn it to position B (dusting and spreading mode).
  
• Thoroughly clean the plastic pins and the sealing face on the solution container – check that there is no residue.
  
• N Thoroughly clean the holes and sealing face on the metering unit (4) – check that there is no residue.
• N Fit the solution tank on the metering unit's housing (4).
• Hook the lever (3) over the bar (5) on the solution container.
  
• Press the levers (3) down until the tabs (2) snap into their seats (6) on the housing with a loud click.
  
• Check that the container is firmly seated.

Blower tube

• Insert a screwdriver into the tab (1) of the hose clamp (2) on the control handle.
• Turn the screwdriver clockwise to loosen the hose clamp (2).
• Pull the hose (3) off the stub.
• Rotate the nozzle (4) until the lugs (5) are covered.
  
• Pull the nozzle (4) off the blower tube (6).

Converting back to misblowing mode

The conversion is carried out in the reverse sequence.

Fitting the hose

• Push the hose with clamp (2) over the stub on the control handle.
• Use pliers to squeeze the hose clamp together (2) until the retaining strip engages and locks.

Filling the Container

• The gasket (1) in the cap must be in good condition, lubricated with grease and clean.
  
• Stand the machine on a level surface.
• Do not exceed maximum level of 3.7 gal (14 liters) (arrow).
  

Mistblowing

• Close valve lever (1) for solution feed.
  
• Pour thoroughly mixed spray solution into the container through the strainer.
  
• Fit the cap and tighten it down firmly.

Working

Mistblowing

The metering lever on the SR 450 must be closed when operating in the mistblowing mode – see dusting and spreading mode.

• Adjust discharge rate with the metering knob – see "Metering Unit".
• Open the valve lever – see "Metering Unit".

Deflector screen

Different baffle screens can be fitted to alter the shape and direction of the spray for accurate application of the solution.

Without deflector screen
Spray jet for long distances – maximum spraying range.

• for spraying high plants and large areas
• for maximum penetration of foliage

Fan jet baffle screen
Spray is broadened and softened.

• for treating plants at close range (< 1.5 m)
• reduces damage to plant, especially in sensitive phases of plant growth

45° deflector screen
Diverts spray jet at an angle of 45°

• for under-leaf treatment
• to increase discharge rate when spraying upwards
• for targeted treatment of lowgrowing crops. Helps reduce problem of spray mist being carried away by the wind when spraying downwards.

Dual deflector screen
Splits the spray jet in two directions.

• Allows two closely planted rows to be treated simultaneously.

After Finishing Work

Emptying the solution container

• Close the valve lever.
• Shut off the engine – see "Starting/Stopping the Engine".
• Turn the metering knob (1) to position "E" and collect the remaining solution in a suitable container.
  

Cleaning the solution container

• Rinse and clean the solution container and hose system with clear water.
• Dispose of remaining spray solution and rinsing liquid in accordance with local environmental requirements – follow maker's instructions.
• Allow the machine to dry with the cap removed.

If strainer is dirty:

• Insert a suitable tool (e.g. screwdriver) in the two recesses (arrows) to loosen the strainer (1).
  
• Pull the strainer (1) upward and out of the solution container.
• Clean the strainer (2) with clear water and a brush.
  

After dusting and spreading

SR 450 only

• Run the unit until the solution container is completely empty N Close the metering lever.
• Shut off the engine – see "Starting/Stopping the Engine".
• Rinse and clean the solution container with clear water.
• Dispose of any residual rinsing solution in accordance with environmental requirements – follow instructions of the chemical manufacturer.
• Allow the machine to dry with the cap removed.

Storing the Machine

• Store the machine in a dry, high or locked location sheltered from frost – out of the reach of children and other unauthorized persons.

For periods of 3 months or longer

• Drain and clean the fuel tank in a well ventilated area.
• Dispose of fuel properly in accordance with local environmental requirements.
• Run the engine until the carburetor is dry – this helps prevent the carburetor diaphragms sticking together.
• Thoroughly clean the machine – pay special attention to the cylinder fins and air filter.
• Do not expose the container to direct sunlight for unnecessarily long periods. UV rays can make the container material brittle, which could result in leaks or breakage.

Engine Management

Exhaust emissions are controlled by the design of the fundamental engine parameters and components (e.g. carburation, ignition, timing and valve or port timing) without the addition of any major hardware.

Replacing the Air Filter

Dirty air filters reduce engine power, increase fuel consumption and make starting more difficult.

If there is a noticeable loss of engine power

• Turn the choke knob to .
• Loosen the screws (1).
• Remove the filter cover (2).
• Remove the filter element (3).
  
• Replace dirty or damaged filters.
• Fit the new filter in the filter housing.
• Fit the filter cover.
• Fit the screws and tighten them down firmly.

Adjusting the Carburetor

General Information
The carburetor comes from the factory with a standard setting.
This setting provides an optimum fuel-air mixture under most operating conditions.

Preparations

• Shut off the engine.
• Check the air filter and clean or replace if necessary.
• Check that the throttle cable is properly adjusted – readjust if necessary – see chapter on "Adjusting the Throttle Cable".
• Check the spark arresting screen (not in all models, country-specific) in the muffler and clean or replace if necessary.
• Turn high speed screw (H) counterclockwise as far as stop (no more than 3/4 turn).
  
• Turn the low speed screw (L) clockwise as far as stop, then turn it back 3/4 turn.

Adjusting Idle Speed

• Carry out the standard setting.
• Start and warm up the engine.

Engine stops while idling

• Turn the idle speed screw (LA) slowly clockwise until the engine runs smoothly.

Erratic idling behavior, engine stops even though setting of LA screw has been corrected, poor acceleration
Idle setting is too lean

• Turn the low speed screw (L) counterclockwise, no further than stop, until the engine runs and accelerates smoothly.

Erratic idling behavior
Idle setting is too rich

• Turn the low speed screw (L) clockwise, no further than stop, until the engine runs and accelerates smoothly.

It is usually necessary to change the setting of the idle speed screw (LA) after every correction to the low speed screw (L).

Fine Tuning for Operation at High Altitude

A slight correction of the setting may be necessary if the engine does not run satisfactorily:

• Carry out the standard setting.
• Warm up the engine.
• Turn high speed screw (H) slightly clockwise (leaner) – no further than stop.

NOTICE
After returning from high altitude, reset the carburetor to the standard setting.
If the setting is too lean there is a risk of engine damage due to insufficient lubrication and overheating.

Spark Plug

If the engine is down on power, difficult to start or runs poorly at idling speed, first check the spark plug.
Install a new spark plug after approx. 100 operating hours or earlier if the electrodes are badly eroded/corroded.
The wrong fuel mix (too much engine oil in the gasoline), a dirty air filter and unfavorable running conditions (mostly at part throttle etc.) affect the condition of the spark plug. These factors cause deposits to form on the insulator nose which may degrade performance.

Removing the spark plug

• Pull off the spark plug boot (1) vertically.
  
• Unscrew the spark plug (2).
• Clean dirty spark plug.
• Check electrode gap (A) and readjust if necessary – see chapter "Specifications."
  
• Use only resistor type spark plugs of the approved range.

Rectify problems which have caused fouling of spark plug:

• too much oil in fuel mix,
• dirty air filter,
• unfavorable running conditions, e.g. operating at part load.

To reduce the risk of fire and burn injury, use only spark plugs authorized by STIHL. Always press the spark plug boot (1) snugly onto the spark plug terminal (2).
Do not use a spark plug with a detachable SAE adapter terminal (3). Arcing may occur that could ignite combustible fumes and cause a fire. This can result in serious injuries or damage to property.

• Only use resistor type spark plugs with solid, non-threaded terminals

Installing the spark plug

• Screw home the spark plug, fit the boot and press it down firmly.

Engine Running Behavior

If engine running behavior is unsatisfactory even though the air filter is clean and the carburetor is properly adjusted, the cause may be the muffler.
Have the muffler checked for contamination (carbonization) by your servicing dealer.
STIHL recommends that you have servicing and repair work carried out exclusively by an authorized STIHL servicing dealer.

Inspections and Maintenance by Dealer

Spark Arrestor in Muffler and Spacer

• If the engine is down on power, have the spark arrestor in the muffler checked.
• Check spacer for damage.
  
• Have damaged spacer replaced immediately.

Maintenance and Care

Main Parts

Definitions

1. Container Cap
   For closing the container.
2. Container
   Contains the material to be sprayed.
3. Lever²⁾
   Locates the container in position onto the metering unit.
4. Metering Unit²⁾
   Allows to operate in mistblowing mode, or dusting and spreading mode.
5. Spark Plug Boot
   Connects the spark plug with the ignition lead.
6. Carburetor Adjusting Screws
   For tuning the carburetor.
7. Manual Fuel Pump
   Provides additional fuel feed for a cold start.
8. Choke Knob
   Eases engine starting by enriching mixture.
9. Starter Grip
   The grip of the pull starter, for starting the engine.
10. Fuel Filler Cap
    For closing the fuel tank.
11. Fuel Tank
    For fuel and oil mixture.
12. Muffler with Spark Arresting Screen
    Muffler reduces engine exhaust noises and diverts exhaust gases away from operator. Spark arresting screen is designed to reduce the risk of fire.
13. Antistatic System²⁾
    Reduces the risk of sparking, when applying any dry substance.
14. Baffle Screen
    To vary the direction and shape of the spray.
15. Metering Knob
    For varying the spraying rate.
16. Nozzle
    Mounted on blower tube, directs airstream.
17. Blower Tube
    Directs the airstream.
18. Throttle Trigger
    Controls the speed of the engine.
19. Control Handle
    Handle on the flexible hose to hold and direct the tube in the required direction, held by the right hand.
20. Setting Lever
    For run and stop. Sets the throttle to various positions or stops the engine.
21. Valve Lever for Solution Feed
    Opens and closes spray liquid hose.
22. Throttle Trigger Lockout¹⁾
    Must be depressed before the throttle trigger can be activated.
23. Metering Lever for Dusting and Spreading Mode²⁾
    For infinitely varying the discharge rate.
24. Pleated Hose
    For blowing in the desired direction.
25. Harness
    For carrying the unit.
26. Backplate
    Helps protect the back of the user.
27. Back Padding, small¹⁾
    Increases carrying comfort.
    1. Back Padding, large¹⁾
       Increases carrying comfort.
28. Intake Screen
    Helps prevent leaves entering intake.
29. Air Filter
    Prevents dust and foreign matter from entering the carburetor.
30. Spacer
    Designed to reduce the risk of burns and fire.

# Serial Number

1. not Fitted on all Markets
2. only SR 450

Specifications

EPA/CEPA
The Emission Compliance Period referred to on the Emissions Compliance Label indicates the number of operating hours for which the engine has been shown to meet Federal emission requirements.
Category

1. = 300 hours
2. = 125 hours
3. = 50 hours

CARB
The Emission Compliance Period used on the CARB-Air Index Label indicates the terms:
Extended = 300 hours
Intermediate = 125 hours
Moderate = 50 hours

Engine
STIHL single cylinder two-stroke engine

Ignition System
Electronic magneto ignition

Fuel System
All position diaphragm carburetor with integral fuel pump
Fuel tank capacity: 57.5 fl oz (1.7 l)

Blowing Performance

Spraying Attachment

Weight

Maintenance and Repairs

Users of this unit should carry out only the maintenance operations described in this manual. STIHL recommends that other repair work be performed only by authorized STIHL servicing dealers using genuine STIHL replacement parts.
Genuine STIHL parts can be identified by the STIHL part number, the logo and, in some cases, by the STIHL parts symbol . The symbol may appear alone on small parts.
For repairs of any component of this unit's air emissions control system, please refer to the air emissions systems warranty in this manual.