Stihl TS420 Manual: A Comprehensive Guide
Recent reports detail issues with Stihl chainsaws, including stalling, hard starting, and spark ignition failures.
Troubleshooting often involves carburetor cleaning, fuel filter checks, and potential coil replacement,
especially after encountering issues with models like the MS 250, MS 231, and MS 171.
The Stihl TS420 is a high-performance cut-off machine, widely recognized for its robust construction and efficiency in demanding applications. This manual serves as a comprehensive resource for owners and operators, providing detailed instructions on safe operation, maintenance, and repair. Understanding the TS420’s capabilities and limitations is crucial for maximizing its lifespan and ensuring optimal performance.

Recent online discussions highlight common issues experienced by Stihl chainsaw users, which, while pertaining to different models, underscore the importance of diligent maintenance applicable to the TS420 as well. These include carburetor problems (ZAMA C1Q and Walbro WT-215), ignition failures, and difficulties with starting after warming up. Addressing these potential concerns proactively through regular inspections and preventative maintenance will minimize downtime and extend the machine’s operational life.
This guide will cover everything from initial assembly and fueling procedures to advanced troubleshooting techniques. Whether you’re a professional contractor or a homeowner tackling occasional projects, this manual will empower you to confidently operate and maintain your Stihl TS420.

Safety Precautions and Warnings
Operating the Stihl TS420 cut-off machine involves inherent risks. Prioritizing safety is paramount to prevent serious injury. Always wear appropriate personal protective equipment (PPE), including safety glasses, hearing protection, gloves, and sturdy footwear. Avoid loose clothing and jewelry that could become entangled in moving parts.
Be acutely aware of your surroundings and ensure a clear work area, free from obstructions and bystanders. Never operate the TS420 in enclosed spaces or near flammable materials. Recent reports of Stihl chainsaw issues – like unexpected stalling or ignition failures – emphasize the need for consistent machine checks before each use. A malfunctioning machine presents an elevated safety hazard.
Inspect the cutting wheel for cracks or damage before operation. Never remove or disable any safety devices. Understand the kickback potential and maintain a firm grip on the machine at all times. Disconnect the spark plug wire before performing any maintenance or repairs. Improper handling can lead to severe consequences; adhere strictly to these warnings.

TS420 Components and Parts Identification
The Stihl TS420 consists of several key components crucial for its operation and maintenance. These include the engine, responsible for power generation; the cutting wheel guard, providing essential operator protection; and the spindle lock, facilitating wheel changes. The fuel tank and oil tank store the necessary fluids for combustion and chain lubrication, respectively.
Essential parts for regular inspection and potential replacement are the air filter, spark plug, and fuel filter. The carburetor regulates the fuel-air mixture, and issues reported with Stihl equipment – such as stalling or difficulty starting – often trace back to carburetor problems. The clutch engages and disengages power to the cutting wheel.
Furthermore, the TS420 features a throttle control, a recoil starter, and various screws, bolts, and washers securing the assembly. Familiarizing yourself with these components, as well as understanding their function, is vital for effective maintenance and troubleshooting, mirroring the diagnostic approach needed for reported Stihl chainsaw issues.
Assembly Instructions
Prior to initial use, careful assembly of the Stihl TS420 is essential for safe and efficient operation. Begin by attaching the wheel guard securely, ensuring it’s properly aligned to deflect debris. Next, mount the cutting wheel, utilizing the spindle lock to facilitate tightening – verify it’s firmly secured before releasing the lock.
Connect the handles to the main unit, tightening all bolts to the manufacturer’s specified torque. Double-check all connections for stability, as loose components can lead to operational issues, similar to the reported problems with Stihl chainsaws experiencing loose clutches or ignition failures.
Inspect and attach any additional accessories, such as extension handles or vacuum attachments, following the provided diagrams. Finally, confirm the fuel and oil tanks are correctly positioned and secured. A thorough assembly check, mirroring the detailed diagnostics needed for carburetor or spark plug issues, ensures optimal performance and longevity of your TS420.
Fueling and Mixing Ratios
Proper fuel mixture is critical for the Stihl TS420’s performance and longevity, preventing issues like stalling or hard starting, commonly reported in other Stihl models. Always use fresh, high-quality unleaded gasoline with a minimum octane rating of 87. The recommended fuel-to-oil ratio is 50:1, utilizing a high-grade 2-stroke engine oil specifically formulated for air-cooled engines.
To achieve the correct mixture, carefully measure the oil and gasoline, then thoroughly combine them in a clean, approved fuel container. Avoid using outdated fuel or mixtures, as they can cause engine deposits and operational problems, mirroring the carburetor issues seen in the MS 250.
Before fueling, ensure the TS420 is switched off and cooled down. Fill the fuel tank slowly, avoiding spills, and securely close the fuel cap. Regularly check the fuel level and maintain the correct mixing ratio for consistent, reliable operation, similar to maintaining proper spark ignition for optimal performance.
Starting Procedures – Cold & Warm Engine
Successfully starting your Stihl TS420 requires specific procedures for both cold and warm engines, addressing potential issues like those experienced with the MS20, which can fail to start when warm. For a cold start, ensure the choke is engaged and the throttle is set to the starting position.
Firmly grasp the starter handle and pull briskly. Repeat several times until the engine attempts to start. Once it sputters, disengage the choke gradually. For a warm start, the choke should remain disengaged. Pull the starter cord with a firm, steady motion. If the engine doesn’t start after several attempts, check the spark plug and fuel supply, mirroring troubleshooting steps for the MS231.
Always maintain a secure grip on the TS420 during starting, and never start the engine if fuel has spilled. Consistent application of these procedures will minimize starting difficulties and ensure reliable operation, preventing issues like those seen with the MS171.
Operating Instructions – Cutting Techniques
Effective cutting with the Stihl TS420 demands proper technique to maximize efficiency and minimize risk, addressing potential issues like chain dulling or engine strain, similar to those reported with the MS250 when encountering tough material. Always maintain a firm grip with both hands, keeping a safe distance from the cutting blade.
Begin cuts with a smooth, controlled motion, allowing the blade to engage gradually. Avoid forcing the cut, as this can lead to kickback or damage. When cutting thicker materials, utilize a progressive cutting approach, gradually increasing the depth of the cut; Be mindful of the material’s reaction, similar to observing how the MS231 responds to different wood densities.

Regularly inspect the blade for sharpness and damage. Proper cutting technique, combined with consistent maintenance, will ensure optimal performance and longevity of your TS420, preventing issues like those experienced with the MS171 during heavy use.
Chain Tensioning and Adjustment
Maintaining correct chain tension is crucial for safe and efficient operation of the Stihl TS420, preventing issues akin to those seen with the MS250 when encountering resistance during cutting. A properly tensioned chain ensures smooth operation, reduces wear, and minimizes the risk of derailment.

To adjust chain tension, first ensure the engine is off and the spark plug is disconnected. Locate the chain tensioning screw, typically found on the side of the saw. Loosen the screw and use the tensioning nut to adjust the chain’s tightness. The chain should be snug against the bar, with minimal sag on the underside.
Avoid over-tensioning, as this can cause excessive wear and heat buildup, similar to the strain experienced by the MS231 when cutting dense materials. After adjustment, tighten the tensioning screw securely. Regularly check and readjust the chain tension, especially after initial use or significant operation, mirroring the maintenance needed for the MS171.
Bar and Chain Maintenance
Consistent bar and chain maintenance is paramount for the longevity and performance of your Stihl TS420, preventing issues like those observed with the MS250 when encountering stubborn branches. Regular upkeep ensures smooth cutting, reduces wear, and enhances safety.
After each use, thoroughly clean the bar and chain with a brush and appropriate cleaning solution, removing sawdust and debris. Inspect the chain for damage, including cracked or dull cutters, and replace as needed. Sharpen the chain regularly using a file or chain grinder, maintaining the correct cutting angles.
Periodically check the bar for wear and burrs, and dress it with a flat file. Ensure the bar oiler is functioning correctly, providing adequate lubrication to the chain during operation, similar to the lubrication needs of the MS231 during prolonged use. A well-maintained bar and chain contribute significantly to the TS420’s efficiency and prevent issues like those seen with the MS171.
Air Filter Cleaning and Replacement
Maintaining a clean air filter is crucial for optimal engine performance of your Stihl TS420, preventing issues akin to the stalling experienced with the MS20 after warming up. A clogged air filter restricts airflow, leading to reduced power, increased fuel consumption, and potential engine damage.
Regularly inspect the air filter after each use, or more frequently in dusty conditions. Remove the filter cover and carefully clean the filter element. For foam filters, wash in warm, soapy water, rinse thoroughly, and allow to dry completely before re-oiling with air filter oil. For felt or nylon filters, tap gently to remove loose debris or use compressed air, blowing from the inside out.
Replace the air filter when it becomes damaged or excessively dirty, ensuring proper engine ventilation. Neglecting this maintenance can lead to problems similar to those reported with the MS231, where a dirty filter contributes to poor running. Consistent air filter maintenance is vital for the TS420’s longevity and efficient operation.
Spark Plug Inspection and Replacement
A properly functioning spark plug is essential for reliable starting and smooth engine operation of your Stihl TS420, mirroring the ignition issues seen in some Stihl MS231 models. Regularly inspect the spark plug for signs of wear, fouling, or damage. A faulty spark plug can cause hard starting, misfiring, and reduced power, similar to the stalling reported with the MS20 after it heats up.
To inspect, disconnect the spark plug wire and carefully remove the spark plug using a spark plug wrench. Examine the electrode for carbon buildup, oil residue, or physical damage. Clean a lightly fouled plug with a wire brush, ensuring the gap remains correct (refer to the technical specifications). Replace the spark plug if it’s heavily fouled, cracked, or damaged.
When installing a new spark plug, ensure it’s properly gapped and tightened to the specified torque. Incorrectly gapped or loose spark plugs can lead to performance issues and potential engine damage, echoing the problems encountered with the MS171’s difficult starting. Consistent spark plug maintenance is key for optimal TS420 performance.

Carburetor Adjustment
Proper carburetor adjustment is crucial for optimal engine performance, mirroring the frequent carburetor concerns reported with Stihl chainsaws like the MS 250 and MS231. Incorrect settings can lead to issues such as hard starting, stalling, poor idling, and reduced power, similar to the MS20’s tendency to stall when warm.
The carburetor controls the air-fuel mixture entering the engine. Adjustments typically involve the idle speed screw, the high-speed screw (H), and the low-speed screw (L). Caution: Carburetor adjustments should only be performed by experienced users or qualified technicians.
Start by ensuring the air filter is clean and the spark plug is in good condition. Begin with the idle speed adjustment, setting it to the manufacturer’s specifications. Then, carefully adjust the high and low-speed screws to achieve smooth acceleration and optimal engine performance. Refer to the technical specifications for precise adjustment procedures. Improper adjustments can worsen performance and potentially damage the engine, as seen in cases of fuel mixture imbalances.
Troubleshooting Common Issues (Stalling, Hard Starting)
Stalling and hard starting are frequent concerns with Stihl equipment, echoing issues reported with models like the MS 20, MS 231, and MS 250. Several factors can contribute to these problems, requiring a systematic approach to diagnosis.

For stalling: Check the fuel filter for clogs, inspect the spark plug for fouling, and verify the carburetor isn’t obstructed – mirroring solutions for the MS231’s ignition problems. A dirty air filter can also restrict airflow, causing stalling. For hard starting: Ensure fresh fuel is used and the correct fuel-oil mixture is maintained. A weak spark plug or a faulty ignition coil can also hinder starting, similar to the MS231’s spark issues.
If the engine starts but immediately stalls, suspect a carburetor issue or a blocked fuel line. If it cranks but doesn’t start, investigate the ignition system. Remember to consult the technical specifications and safety precautions before attempting any repairs. Consistent issues may indicate a need for professional servicing, as seen with blocked BMS batteries.
Storage and Transportation
Proper storage and transportation are crucial for maintaining the Stihl TS420’s longevity and ensuring safe operation. Before long-term storage, thoroughly clean the unit, removing any debris or accumulated residue. Drain the fuel tank completely to prevent fuel degradation and carburetor issues, mirroring preventative measures for models like the MS 250.
For transportation: Always engage the chain brake and utilize a scabbard to protect the bar and chain. Secure the TS420 properly in a vehicle to prevent movement during transit. Avoid transporting the unit with fuel in the tank, if possible, or ensure the fuel cap is tightly sealed to prevent leaks.

Store the TS420 in a dry, well-ventilated area, away from direct sunlight and extreme temperatures. Periodically check the unit for any signs of corrosion or damage. Following these guidelines will help preserve the TS420’s performance and reliability, preventing issues like those encountered with blocked batteries or ignition failures.
Technical Specifications
The Stihl TS420 is a high-performance cut-off machine designed for demanding professional applications; Its displacement is 76.5 cc (4.66 cu. in.), powered by a 2-stroke engine. The power output reaches 4.4 kW (5.9 hp), providing ample cutting force. Fuel capacity is 0.75 liters (0.198 US gal), and the oil capacity for the chain lubrication system is 0.26 liters (0.069 US gal).

Weight (without cutting wheel): 9.5 kg (20.9 lbs). The TS420 utilizes a centrifugal clutch for smooth engagement and disengagement. Maximum cutting depth is 130 mm (5.1 in). The anti-vibration system minimizes operator fatigue during extended use, addressing concerns similar to those found in models like the MS 171.
Ignition system: Fully electronic. The TS420’s robust construction and precise engineering ensure reliable performance and durability. Regular maintenance, as outlined in this manual, is essential to uphold these specifications and prevent issues like carburetor malfunctions or spark ignition failures, mirroring preventative care for other Stihl products.


























