How to String a Fs40c Stihl Weed Eater? Easy Spool Loading

Introduction

Knowing how to string a FS40C Stihl Weed Eater properly can save you time, money, and frustration. Whether you are dealing with a tangled mess of line or preparing for routine maintenance, understanding the spool loading process is essential for keeping your trimmer running smoothly. The FS40C model uses a semi-automatic feed system that requires careful attention to line tension and spool alignment. This guide walks you through every step of the process, from identifying the correct string type to troubleshooting common issues that prevent proper line advancement.

• Tools and Materials Needed
• Understanding the FS40C Spool System
• Identifying the Correct String Type
• Preparing Your Trimmer for Stringing
• Removing Old String Completely
• Master Spool Loading Technique
• Feeding the Line Through the Cleat
• Testing Line Feed Mechanism
• Troubleshooting Common Problems
• String and Spool Comparison Table
• Maintenance Tips and Best Practices
• Common Mistakes to Avoid
• Frequently Asked Questions
• Conclusion

Tools and Materials Needed

Before beginning the spool loading process, gather these essential items to ensure a smooth procedure. Having everything ready prevents interruptions and reduces the risk of forcing components that should move freely.

• Stihl FS40C replacement string (typically 2.0mm or 2.4mm diameter)
• Small flathead screwdriver
• Clean cloth or paper towels
• Scissors or utility knife
• Work gloves for hand protection

The correct string diameter is crucial for proper operation. Using string that is too thick can cause feeding problems, while string that is too thin may break frequently during use.

Understanding the FS40C Spool System

The FS40C features a semi-automatic line feed mechanism housed within a plastic spool assembly. Unlike bump-feed systems that require tapping the ground, this model advances line automatically when the engine reaches operating speed. The spool contains two critical components: the line itself and a spring-loaded tension mechanism that controls how much line extends during operation.

The spool sits inside the cutting head housing and rotates freely when the trigger is engaged. A small metal cleat or hook holds one end of the string in place, preventing it from slipping back into the housing during normal operation. Understanding how these components interact helps explain why proper tension and alignment matter so much for reliable performance.

Identifying the Correct String Type

Stihl recommends specific string diameters for different applications and models. For the FS40C, the most commonly used options include:

1. 2.0mm round string – Best for light-duty trimming around delicate plants and small areas
2. 2.4mm round string – Standard choice for general-purpose trimming of grass and weeds
3. Square or star-shaped string – More aggressive cutting but wears faster on hard surfaces

Always check your owner’s manual or the specifications printed on the existing string before purchasing replacements. Using the wrong size can lead to poor cutting performance, excessive wear on internal components, or frequent line breakage.

Preparing Your Trimmer for Stringing

Safety comes first when working with power tools. Follow these preparation steps before attempting to remove or install string:

1. Disconnect the spark plug wire to prevent accidental starting during maintenance
2. Drain excess fuel if the tank is nearly full, reducing fire hazard and spillage risk
3. Place the trimmer on a stable work surface such as a workbench or sturdy table
4. Remove the air filter cover if it interferes with accessing the cutting head
5. Inspect the cutting head housing for cracks, debris, or damaged components

Taking these precautions protects both you and your equipment throughout the stringing process.

Removing Old String Completely

Proper removal of old string prevents tangles and ensures clean installation of new line. Follow this systematic approach:

1. Locate the release button on the side of the cutting head housing
2. Press the release button while simultaneously pulling the spool upward
3. Remove the entire spool assembly from the housing carefully
4. Pull out all remaining old string from both sides of the spool
5. Clean the spool groove with a cloth to remove any debris or residue
6. Check the spring mechanism inside the spool for damage or binding

If the old string is severely tangled, you may need to cut it away in sections rather than trying to unwind it completely. Always remove every piece to avoid interference with new line installation.

Master Spool Loading Technique

Correct spool loading requires patience and attention to detail. The winding direction and tension affect how smoothly the line feeds during operation.

Start by cutting approximately 3 meters (10 feet) of new string. This length provides enough line for normal use without creating excessive bulk in the spool. Tie a simple overhand knot at one end of the string, leaving about a 5-centimeter tail.

Place the knotted end into the small hole found in the center hub of the spool. Some models feature a dedicated notch or slot designed specifically for securing the starting end of the string. Wind the line onto the spool in the direction indicated by arrows molded into the plastic. Winding against these arrows creates excessive tension that prevents proper line advancement.

Maintain moderate tension while winding by gently pulling the string as you rotate the spool. Over-tightening causes the line to bind, while loose winding allows tangles to form during storage. Fill the spool groove evenly without overlapping layers, which can create uneven feeding characteristics.

Feeding the Line Through the Cleat

Once the spool contains properly wound string, reinstall it into the cutting head housing:

1. Align the spool tabs with corresponding slots in the housing
2. Insert the spool by pressing it firmly into place until it clicks
3. Rotate the spool slightly to ensure proper seating
4. Pull approximately 15 centimeters of string through the cutting edge slot
5. Hook the loose end onto the metal cleat or retention mechanism
6. Give the string a gentle tug to confirm secure attachment

The cleat serves as an anchor point that prevents the entire line from retracting into the housing during trimming. Make sure the string sits properly in the grooves on both sides of the cutting head for balanced operation.

Testing Line Feed Mechanism

After installation, verify that the automatic feed system functions correctly:

1. Reconnect the spark plug wire only after completing all mechanical checks
2. Start the trimmer and let it reach normal operating speed
3. Engage the cutting head briefly to observe line behavior
4. Check for smooth rotation without binding or hesitation
5. Verify equal line length extending from both sides of the head

If the line fails to advance or feeds unevenly, shut off the engine immediately and investigate the cause before continuing use.

Troubleshooting Common Problems

Even experienced users encounter occasional issues when stringing their FS40C. Here are solutions to the most frequent problems:

Line Not Advancing Automatically

This issue typically stems from one of three causes. First, insufficient string length extending through the cutting slot prevents the sensor from triggering line release. Ensure at least 10 centimeters extends freely on each side.

Second, winding the string too tightly during spool loading restricts movement within the housing. Remove and rewind with lighter tension.

Third, debris accumulation in the feed mechanism blocks normal operation. Clean the cutting head housing thoroughly with compressed air or a soft brush.

String Tangling During Use

Tangles usually result from improper winding technique or using damaged string. Always wind in the direction indicated by spool arrows and replace frayed or kinked line immediately.

Uneven line lengths also contribute to tangling. Before each use, manually adjust both ends so they extend equal distances from the cutting head.

Excessive Wear on Specific Areas

If your string wears out quickly in certain spots, examine your trimming technique. Holding the trimmer at extreme angles or pressing too hard against surfaces accelerates wear unnecessarily.

Consider switching to a more durable string type for challenging conditions, but never exceed the manufacturer’s recommended diameter specifications.

String and Spool Comparison Table

Different string types serve distinct purposes and offer varying performance characteristics. Choose based on your typical trimming conditions and frequency of use.

Maintenance Tips and Best Practices

Implementing regular maintenance habits extends the life of your FS40C and reduces the frequency of stringing procedures:

• Inspect string condition daily before each use, replacing frayed sections immediately
• Keep spare spools pre-wound for quick replacement during extended work sessions
• Store extra string in a cool, dry location away from direct sunlight to prevent degradation
• Clean the cutting head after each major project removing grass clippings and debris that interfere with line movement
• Check the retention spring periodically ensuring it maintains proper tension without binding
• Use appropriate trimming techniques avoiding excessive pressure that accelerates string wear

These practices minimize downtime and maintain consistent cutting performance throughout the growing season.

Common Mistakes to Avoid

New users often make preventable errors that complicate the stringing process or damage equipment:

Using Incorrect String Diameter

Installing string that is too thick or too thin creates operational problems ranging from poor cutting efficiency to premature component failure. Always verify specifications in your owner’s manual before purchasing replacements.

Ignoring Wind Direction Arrows

The arrows molded into the spool indicate the proper winding direction. Installing string against these markings results in excessive tension that prevents automatic line advancement.

Over-Tightening During Winding

While maintaining adequate tension prevents loose coils, over-tightening restricts line movement and causes frequent feeding failures. Aim for firm but flexible winding pressure.

Skipping Housing Cleaning

Debris accumulation in the cutting head housing interferes with spool rotation and line advancement. Take time to clean components thoroughly during each stringing procedure.

Frequently Asked Questions

What string diameter works best with the FS40C?

The FS40C performs optimally with 2.0mm to 2.4mm diameter string. The 2.4mm size handles most general trimming tasks effectively, while 2.0mm works better for lighter duty applications around delicate plants.

Which direction should I wind the string on the spool?

Always wind in the direction indicated by arrows molded into the spool surface. These arrows ensure proper tension and alignment that allows the automatic feed mechanism to function correctly.

How much string should extend through the cutting slot?

Allow approximately 15 centimeters (6 inches) of string to extend through the cutting slot on each side. Too little prevents proper feeding, while too much increases the risk of tangles.

How often should I rewind the spool?

Rewind whenever you notice reduced cutting performance, frequent line breakage, or visible wear on the string. For heavy use, inspect the line before each session and rewind as needed.

Do I need to disconnect the spark plug during stringing?

Yes, always disconnect the spark plug wire before performing any maintenance on your FS40C. This safety precaution prevents accidental starting that could cause injury or equipment damage.

Why does my string tangle immediately after installation?

Tangling typically results from improper winding technique or using damaged string. Ensure you wind in the correct direction with moderate tension, and replace any kinked or frayed line before installation.

Can I use alternative line types like trimmer line from other brands?

While many universal trimmer lines are compatible, using Stihl-approved string ensures optimal performance and longevity. Third-party alternatives may work but often lack the quality consistency of genuine Stihl products.

Conclusion

Mastering how to string a FS40C Stihl Weed Eater properly transforms what could be a frustrating maintenance task into a straightforward procedure. By following the systematic approach outlined in this guide, you can achieve reliable line feeding, reduce downtime, and extend the overall lifespan of your trimming equipment. Remember to always prioritize safety by disconnecting the spark plug, use the correct string diameter for your application, and maintain moderate tension when winding the spool.

Regular inspection and timely replacement of worn string prevents unexpected failures during critical work periods. Developing good maintenance habits, such as cleaning the cutting head housing and keeping spare pre-wound spools ready, ensures you stay productive throughout the season. With practice, the entire spool loading process should take less than ten minutes, allowing you to return to your trimming tasks quickly and confidently.

The investment in learning proper stringing techniques pays dividends in improved cutting performance and reduced equipment wear. Whether you are maintaining a small garden or managing larger landscaping projects, these skills form the foundation of effective trimmer ownership. Keep this guide handy for reference during future maintenance sessions, and your FS40C will continue delivering reliable performance for years to come.