How to Change Stihl Fs38 Weed Eater String? Pro Tips

Introduction

The Stihl Fs38 is a popular, lightweight gas-powered string trimmer favored by homeowners and DIY landscapers for its ease of use and reliable performance. One of the most basic but essential maintenance tasks for this tool is replacing the trimmer string when it wears out, breaks, or stops feeding properly. Many users assume this task requires professional help, but learning How to Change Stihl Fs38 Weed Eater String? is a simple, 10-minute process that saves you money on repairs and keeps your trimmer running at peak performance. This comprehensive guide walks you through every step of the process, from identifying when to replace the string to pro tips for extending its lifespan, plus troubleshooting common issues you may encounter along the way.

• Understanding Your Stihl Fs38 Weed Eater
• Key Components of the Fs38 Trimmer Head
• When to Replace Your Stihl Fs38 Weed Eater String
• Tools and Materials You’ll Need
• Step-by-Step Guide to Changing Stihl Fs38 Weed Eater String
• String Type Comparison: Which Is Best for Your Fs38?
• Pro Tips for Extending String Life and Improving Performance
• Common Mistakes to Avoid When Changing Stihl Fs38 Weed Eater String
• Troubleshooting Common Post-Replacement Issues
• Frequently Asked Questions
• How Often Should I Change the String on My Stihl Fs38?
• What Size String Does the Stihl Fs38 Use?
• Can I Use Third-Party String Instead of OEM Stihl String?
• Why Is My New String Not Feeding Properly After Replacement?
• Conclusion

Understanding Your Stihl Fs38 Weed Eater

The Stihl Fs38 is part of Stihl’s line of compact, user-friendly gas trimmers designed for residential use. It features a 1.5 horsepower engine, a 16-inch cutting swath, and a lightweight design that weighs just 10.6 pounds, making it easy to maneuver for extended periods. Unlike larger commercial trimmers, the Fs38 uses a bump-feed trimmer head that releases string automatically when you tap the head against the ground, eliminating the need to manually advance the line during use. This design makes it ideal for homeowners with small to medium-sized lawns, garden beds, and walkways. Understanding how the trimmer head works is the first step to mastering How to Change Stihl Fs38 Weed Eater String? correctly.

Key Components of the Fs38 Trimmer Head

The Fs38’s trimmer head is a simple but precise mechanism made up of a few key parts you’ll interact with during string replacement. First, the spool is the cylindrical component that holds the trimmer string, with a small central hole for inserting the string end and notches to keep the string in place while winding. The bump knob is the rubber or plastic piece on the bottom of the head that you tap against the ground to release more string; it connects to an internal cam that pushes the spool forward to feed out a small length of line. The retention knob or locking tab is a small screw or clip on the bottom of the head that holds the spool in place during use; you’ll loosen this to remove the spool for replacement. Finally, the string itself is the cutting component, designed to wear down gradually as you trim grass and weeds. Familiarizing yourself with these parts will make the replacement process far less intimidating.

When to Replace Your Stihl Fs38 Weed Eater String

Knowing when to replace your trimmer string is just as important as knowing how to install it. Using worn or broken string not only reduces cutting performance, but it can also damage the trimmer head, strain the engine, and leave you with an uneven, messy lawn. There are several clear signs that it’s time to replace your string: first, visible fraying, splitting, or wear along the length of the line, especially near the center of the spool where it experiences the most friction. Second, frequent breakage during normal use, even when trimming soft grass. Third, the string no longer feeds properly when you bump the head, which is often a sign that the string is too short, tangled, or worn out. Fourth, reduced cutting power, where the trimmer struggles to cut through thick weeds or grass that it previously handled easily. As a general rule, inspect your string before each use, and replace it as soon as you notice any of these signs to avoid more costly repairs down the line.

Tools and Materials You’ll Need

Before you start the replacement process, gather all the necessary tools and materials to avoid interruptions. You will need: a replacement trimmer string that matches the manufacturer’s specifications for the Fs38 (we’ll cover size and type options later in this guide), a small flathead screwdriver (to loosen the retention knob if it’s tight), sharp scissors or a dedicated trimmer string cutter (to cut the string to the correct length), work gloves (to protect your hands from sharp string ends and rough trimmer parts), safety glasses (to protect your eyes from flying debris when testing the trimmer), and a small soft brush (to clean grass and dirt out of the trimmer head before reinstalling the spool). Having all these items on hand before you start will make the process faster and safer.

Step-by-Step Guide to Changing Stihl Fs38 Weed Eater String

Now that you’re familiar with your trimmer and have the necessary tools, follow these simple, safe steps to complete the string replacement process. Each step includes safety notes and best practices to ensure you get the best results and avoid common errors.

1. Prepare the weed eater for maintenance: Start by turning off the Fs38’s engine and letting it cool completely if you were using it recently. A hot engine can cause serious burns, so wait at least 15 minutes after shutdown before touching any metal components. Next, disconnect the spark plug wire from the spark plug to prevent accidental starting while you’re working on the trimmer head. This step eliminates the risk of accidental starting and injury. Once the spark plug is disconnected, place the trimmer on a flat, stable work surface, and use a soft brush to clear any grass, dirt, or debris from the trimmer head area to prevent dirt from entering the feed mechanism and causing jams later.
2. Remove the old spool and string: Locate the retention knob on the bottom of the Fs38’s trimmer head. This small plastic or metal knob screws into the center of the head to hold the spool in place. Turn the knob counterclockwise (left) to loosen it—you do not need to remove it completely, just loosen it enough to release the spool. Once the knob is loose, pull the spool straight out of the trimmer head. If it feels stuck, gently wiggle it side to side to loosen it; avoid excessive force to prevent damage to the spool or head’s internal components. Once the spool is removed, pull off any remaining old string and discard it. While the spool is removed, inspect it for cracks, warping, or worn notches; if the spool is damaged, replace it with a new OEM or compatible third-party spool before continuing, as a damaged spool will cause string tangles and feeding issues.
3. Measure and cut the new replacement string: The Fs38 requires a specific length of string to feed properly, typically 10 to 12 feet for standard bump-feed models. Use a tape measure to cut the string to the correct length, or use a pre-cut replacement string roll sized for the Fs38 to avoid measuring errors. Cut the string with sharp scissors for a clean edge; ragged cuts cause tangles. Always wear work gloves when handling cut string ends, as they are extremely sharp and can cause deep cuts. If you’re unsure of the correct length, cut a little extra string (up to 13 feet) rather than too little; excess string can be trimmed later if needed, but too little string will not feed properly.
4. Wind the new string onto the spool correctly: This is the most critical step in the process, as incorrect winding is the most common cause of feeding problems after replacement. First, locate the winding direction indicator on your spool—most Fs38 spools have a small arrow printed on the face that shows the correct winding direction, which is clockwise when looking directly at the spool. Insert one end of the cut string into the small central hole in the spool, leaving 2 to 3 inches of string sticking out of the hole. Hold the end in place with your finger to keep it from slipping out. Then, wind the string tightly and evenly around the spool, following the direction of the arrow. Avoid overlapping the string to prevent tangles and uneven feeding. Keep the string taut as you wind to ensure it sits flush against the spool. Once you’ve wound the entire length of string, leave 6 to 8 inches of string sticking out of the spool as the working end—this is the length that will feed out when you bump the trimmer head. If you wind the string in the wrong direction, the bump mechanism will not be able to push the spool forward to release string, so double-check the arrow indicator before you start winding.
5. Reinstall the spool and test the trimmer: Once the string is wound correctly, align the spool with the slots in the trimmer head, making sure the string ends are positioned in the notches on the outside of the spool that feed into the trimmer head. Push the spool firmly into the head until it clicks into place, then turn the retention knob clockwise (right) to lock it in place. Avoid overtightening to prevent stripped threads or warping. Next, reconnect the spark plug wire to the spark plug. Pull the working end of the string out a few inches, then tap the bump knob against the ground a few times to test the feed mechanism. If the string releases in 2 to 3 inch increments each time you bump the head, the replacement was successful. If the string does not feed, double-check the winding direction and make sure the spool is fully seated in the head. Once you confirm the feed is working, start the trimmer and test it on a small patch of grass to ensure it cuts evenly.

String Type Comparison: Which Is Best for Your Fs38?

Not all trimmer string is created equal, and choosing the right type for your Fs38 will improve cutting performance and extend the life of both the string and your trimmer. The Fs38 is compatible with .080 inch (2.0 mm) diameter string, the most common size for residential trimmers. Below is a comparison of the most popular string types to help you choose the best option for your needs.

Round string is the standard, all-purpose option for most users, offering a good balance of durability and cutting power for general lawn maintenance. Square string has a sharper edge that cuts through thick, woody weeds more effectively, but it wears down faster when used on hard surfaces like concrete or gravel. Serrated string has small teeth along its length that tear through heavy brush and dense vegetation, but it is the least durable option and breaks quickly on abrasive surfaces. OEM Stihl string is manufactured to Stihl’s exact specifications, offering consistent quality and performance, while high-quality third-party string is a cost-effective alternative for casual users. For most Fs38 owners, standard round .080″ string is the best all-around choice, unless you regularly tackle thick, overgrown vegetation.

Pro Tips for Extending String Life and Improving Performance

With a few simple best practices, you can extend the life of your trimmer string and keep your Fs38 running at peak performance for years. First, store extra string in a cool, dry place away from direct sunlight, as UV exposure and moisture can make string brittle and prone to breaking. Second, avoid cutting near hard surfaces like concrete, rocks, or brick, as these surfaces wear down string much faster than soft grass and soil. Third, always wind the string tightly and evenly on the spool, as loose or overlapping string tangles more easily and wears out unevenly. Fourth, use only the manufacturer-recommended .080 inch string size for your Fs38; smaller string will break too quickly, while larger string will overload the engine and reduce cutting power. Fifth, clean the trimmer head regularly to remove built-up grass, dirt, and debris that can jam the feed mechanism and cause string to stick. Finally, keep a pre-wound spare spool on hand for quick swaps if your string runs out mid-job.

Common Mistakes to Avoid When Changing Stihl Fs38 Weed Eater String

Even experienced users make mistakes when replacing trimmer string, but avoiding these common errors will save you time and frustration. The most frequent mistake is winding the string in the wrong direction; always follow the arrow indicator on your spool, as reversed winding will prevent the bump feed mechanism from working. Second, using the wrong string size: never use string smaller or larger than .080 inch for the Fs38, as this can damage the trimmer head, cause frequent breakage, or reduce cutting performance. Third, overlapping the string when winding, which creates bumps that cause tangles and uneven feeding. Fourth, forgetting to disconnect the spark plug before starting work, which can lead to accidental starting and serious injury. Fifth, not leaving enough string sticking out of the spool after winding; if less than 6 inches is exposed, the string will not feed properly when you bump the head. Sixth, using old, frayed, or damaged string for replacement, which will break quickly and may damage the spool’s internal notches.

Troubleshooting Common Post-Replacement Issues

Even if you follow all the steps correctly, you may encounter minor issues after replacing your string. Here are the most common problems and their fixes. First, if the string does not feed when you bump the head: check that you wound the string in the correct direction, that the spool is fully seated and locked in place, and that at least 6 inches of string is exposed. If the problem persists, inspect the bump knob for damage or debris that may be preventing it from engaging the spool. Second, if the string breaks frequently after replacement: confirm you are using the correct .080 inch size, that you are not cutting near hard surfaces, and that the string is wound tightly without overlaps. Low-quality string may also break more easily, so opt for a reputable brand if you’re using third-party line. Third, if the trimmer vibrates excessively after replacement: check that the spool is locked in place, that the string is wound evenly, and that there is no debris stuck in the trimmer head. Excessive vibration may indicate a damaged spool or engine issue; visit a professional if the problem persists. Fourth, if the string tangles inside the spool: unwind all the string, rewind it tightly and evenly in the correct direction, making sure there are no overlaps or kinks. If tangling continues, the spool may be damaged and need replacement.

Frequently Asked Questions

How Often Should I Change the String on My Stihl Fs38?

The frequency of string replacement depends on how often you use your trimmer and the type of vegetation you cut. For average residential use (1 to 2 hours per week cutting grass and soft weeds), replace the string every 1 to 2 months. If you use the trimmer more frequently, or cut thick, abrasive weeds and brush, you may need to replace it every 2 to 3 weeks. Always inspect the string before each use for fraying, wear, or damage, and replace it immediately if you notice any issues to avoid breakage mid-job.

What Size String Does the Stihl Fs38 Use?

The Stihl Fs38 is factory-designed to use .080 inch (2.0 mm) diameter round trimmer string for optimal performance. Some users opt for .065 inch string for lighter, finer trimming tasks, but .080 inch provides the best balance of cutting power and durability for most residential and light commercial use. Always refer to your owner’s manual for the manufacturer’s official recommendations to avoid voiding your warranty or damaging your trimmer.

Can I Use Third-Party String Instead of OEM Stihl String?

Yes, you can use high-quality third-party .080 inch round string with your Fs38, and many casual users do to save money on replacement costs. However, low-quality third-party string may break more frequently, wear out faster, or jam the feed mechanism due to inconsistent diameter or poor material quality. If you choose to use third-party string, opt for a reputable brand with positive user reviews to ensure consistent performance and durability.

Why Is My New String Not Feeding Properly After Replacement?

The most common causes of feeding issues after string replacement are incorrect winding direction, an improperly seated spool, or not leaving enough exposed string. First, confirm you wound the string in the direction indicated by the arrow on the spool (clockwise for most Fs38 models). Second, make sure the spool clicked into place in the trimmer head and the retention knob is fully tightened. Third, ensure at least 6 inches of string is sticking out of the spool after winding. If you’ve checked all these factors and the string still won’t feed, inspect the trimmer head for built-up debris or damaged internal components that may be blocking the feed mechanism.

Conclusion

Learning How to Change Stihl Fs38 Weed Eater String? is a simple, valuable skill that every Fs38 owner should master. By following the step-by-step guide outlined above, using the correct string type, and avoiding common mistakes, you can complete this maintenance task in 10 minutes or less, without needing to visit a professional repair shop. Regular string replacement keeps your trimmer running efficiently, extends its lifespan, and ensures you get clean, even cuts every time you use it. Remember to prioritize safety by disconnecting the spark plug before starting work, inspect your string regularly for wear, and follow the pro tips in this guide to get the most out of your trimmer. With these best practices, your Stihl Fs38 will remain a reliable tool for all your lawn and garden maintenance needs for years to come.