Stihl BR420C Magnum Manual

The Stihl BR420C Magnum is a professional-grade backpack blower designed for heavy-duty clearing and cleanup applications. It features a powerful 2-stroke engine with electronic ignition, a comfortable harness system, variable throttle control, anti-vibration handles, a translucent fuel tank, and a high-velocity air nozzle. Below are key sections for safety, features, operation, maintenance, troubleshooting, and specifications.

1. Features at a Glance 2. Safety Information 3. Assembly & Preparation 4. Specifications 5. Controls and Operation 6. Fuel & Lubrication 7. Starting & Stopping Procedure 8. Maintenance Schedule 9. Storage Guidelines 10. Warranty Information 11. Troubleshooting

Features at a Glance

Key components: 2-stroke engine, backpack frame with harness, throttle trigger, air filter, spark plug, fuel tank, and blower tube.

FeatureDescription
Engine Type2-stroke, single cylinder, air-cooled
Ignition SystemElectronic ignition (CDI)
Displacement64.8 cc (3.95 cu. in.)
Fuel Tank Capacity1.9 L (0.5 US gal)
Air VelocityUp to 320 km/h (199 mph)
Air VolumeUp to 1,200 m³/h (706 cfm)
Sound Power Level112 dB(A)
Weight (dry)10.3 kg (22.7 lbs)
Harness SystemPadded, adjustable backpack harness
Throttle ControlVariable speed trigger with lock

Safety Information

Read all instructions before operation. Wear appropriate PPE.

  1. Personal Protective Equipment: Always wear safety glasses, hearing protection, long pants, sturdy gloves, and non-slip boots.
  2. Operating Area: Keep bystanders and pets at least 15 meters away. Operate only in well-ventilated areas.
  3. Fuel Safety: Refuel in a well-ventilated area with engine stopped and cool. Use only clean, fresh fuel mix.
  4. Hot Surfaces: Avoid contact with muffler and cylinder during and after operation.

WARNING! Risk of fire, explosion, and serious injury. Do not operate near flammable materials or in enclosed spaces.

Assembly & Preparation

Unpack and inspect all parts. Assemble on a clean, flat surface.

  1. Attach Harness: Connect shoulder straps and waist belt to backpack frame; adjust for comfort.
  2. Install Blower Tube: Push tube onto engine outlet until it clicks securely into place.
  3. Fuel Mix: Prepare 50:1 fuel mixture using STIHL 2-stroke oil and 89 octane (or higher) unleaded gasoline.
  4. Fill Fuel Tank: Use funnel to pour fuel mix into translucent tank. Do not overfill.

CAUTION! Ensure all fasteners are tight before operation. Check for fuel leaks.

Specifications

Controls and Operation

Main Controls: Throttle trigger, throttle lock, choke lever, stop switch, master control lever.

Master Control Lever Positions: - STOP (0): Engine off. - START (N): Normal run position for starting. - CHOKE (⏰): Cold start position (choke closed). - RUN (⏵): Warm run position.

Operation: Adjust harness for balanced fit. Start engine on flat ground. Use variable throttle to control airspeed. For continuous operation, engage throttle lock. Always hold unit with both hands.

Fuel & Lubrication

Use only fresh, clean fuel mix. Never use straight gasoline or old fuel.

  1. Mixing: Pour STIHL 2-stroke oil into clean container, then add gasoline. Shake well.
  2. Refueling: Clean area around fuel cap. Fill to marked level. Wipe spills immediately.
  3. Lubrication: Gearbox is factory filled. Check for leaks periodically.

Tip: Use fuel stabilizer if storing for more than 30 days. Never store with fuel in tank for long periods.

Starting & Stopping Procedure

Follow these steps for safe starting.

  1. Cold Start: Place unit on flat ground. Set master control to CHOKE. Press purge bulb 5-6 times. Pull starter rope sharply until engine fires. Move lever to START. Pull starter again until engine runs. Allow brief warm-up.
  2. Warm Start: Set master control to START. Pull starter rope.
  3. Stopping: Release throttle. Move master control to STOP.
  4. Emergency Stop: Immediately move master control to STOP.

WARNING! Keep hands and feet clear of blower tube during starting. Never drop-start the unit.

Maintenance Schedule

Regular maintenance ensures performance and longevity.

IntervalTask
DailyCheck fasteners, clean air filter, inspect for damage
25 HoursClean spark arrestor screen, check spark plug
50 HoursReplace spark plug, clean cooling fins
100 HoursCheck fuel lines, replace air filter, inspect muffler
AnnuallyProfessional servicing recommended

CAUTION! Always disconnect spark plug wire before performing maintenance.

Storage Guidelines

Prepare unit for storage to prevent damage.

  1. Short-term (under 30 days): Run engine dry of fuel or add fuel stabilizer.
  2. Long-term: Drain fuel tank and carburetor completely. Remove spark plug and add 1 tsp of oil into cylinder. Pull starter slowly to distribute oil. Reinstall spark plug. Store in dry, clean place.

CAUTION! Store fuel mix in approved container away from heat sources and open flame.

Warranty Information

STIHL Limited Warranty: 1-year commercial warranty from date of purchase. Proof of purchase required. Warranty covers defects in materials and workmanship. Does not cover normal wear, misuse, improper fuel, or lack of maintenance. For warranty service, contact an authorized STIHL servicing dealer. For support, visit www.stihlusa.com or call 1-800-467-8445.

Troubleshooting

SymptomPossible CauseCorrective Action
Engine will not startNo fuel, flooded, spark plugCheck fuel level; set choke correctly; check/replace spark plug.
Engine runs poorlyDirty air filter, old fuelClean/replace air filter; drain and refill with fresh fuel mix.
Loss of powerClogged spark arrestor, carburetorClean spark arrestor screen; have carburetor adjusted by dealer.
Excessive vibrationLoose parts, damaged impellerTighten all fasteners; inspect impeller for damage.
Airflow reducedClogged tube, worn impellerClear debris from tube; inspect impeller blades.

Dealer Service: For complex issues, take to authorized STIHL dealer.

Support: 1-800-467-8445; www.stihlusa.com

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