How to Start a Stihl Fs38 Weed Eater? Cold & Warm Start Tips

Introduction

If you’ve ever struggled to get your Stihl FS38 weed eater running on the first pull, you’re not alone. This popular, lightweight gas-powered trimmer is a workhorse for residential and light commercial use, but its two-stroke engine requires a specific starting process that differs from standard lawnmowers or other small engines. Whether you’re pulling it out for the first use of the season after winter storage, or starting it up mid-job after a short break, knowing the correct procedure for both cold and warm starts will save you time, frustration, and unnecessary wear on your tool. Many users mistakenly try to start the FS38 the same way they start a four-stroke lawnmower, leading to flooded engines and avoidable frustration. This guide walks you through every step of How to Start a Stihl Fs38 Weed Eater?, including safety prep, step-by-step instructions for both start types, troubleshooting common issues, and best practices to keep your trimmer running reliably for years.

• Understanding Your Stihl FS38 Weed Eater
• Key Components for Starting
• Cold Start vs. Warm Start: Key Differences
• When to Use Each Start Method
• Pre-Start Safety and Preparation Steps
• Step-by-Step Cold Start Guide for the Stihl FS38
• Step-by-Step Warm Start Guide for the Stihl FS38
• Common Starting Issues and Quick Fixes
• Fuel System Problems
• Ignition and Spark Issues
• Best Practices for Reliable Starts Every Time
• Routine Maintenance to Avoid Start Failures
• Frequently Asked Questions
• How Many Pulls Should It Take to Cold Start a Stihl FS38?
• Can I Use Stale Fuel in My Stihl FS38?
• Why Won’t My FS38 Start After Sitting for Months?
• Do I Need to Mix Oil with Gas for My Stihl FS38?
• What Type of Gas Is Best for a Stihl FS38?
• Conclusion

Understanding Your Stihl FS38 Weed Eater

The FS38 is one of Stihl’s most popular lightweight trimmers, known for its low emissions, fuel efficiency, and ease of use, but its two-stroke engine does require a bit more know-how to start than standard four-stroke lawn equipment. Unlike four-stroke engines, its two-stroke design requires a precise fuel-to-oil mixture to lubricate internal parts while running, which is a critical factor in successful starting.

Key Components for Starting

Before you attempt to start the FS38, it helps to familiarize yourself with the key components involved in the starting process:

• Fuel tank: Located on the side of the unit, this holds the pre-mixed fuel and oil blend. It has a vented cap to prevent pressure buildup during operation.
• Primer bulb: A small, rubber bulb near the carburetor that pumps fuel into the engine’s combustion chamber when pressed, making starting easier, especially for cold starts.
• Choke lever: A sliding or rotating lever on the side of the carburetor that restricts airflow to enrich the fuel mixture for cold starts. It has two positions: “choke” (closed) for cold starts and “run” (open) for warm operation.
• Throttle trigger lock: A safety lever behind the main throttle trigger that must be squeezed to engage the throttle during starting.
• Starter cord and handle: The recoil starter on the top of the engine that you pull to crank the engine and initiate combustion.
• Spark plug: Located on the front of the engine, it creates the spark that ignites the fuel-air mixture. A worn or dirty spark plug is one of the most common causes of starting failure.

Understanding how these parts work together will make the starting process far less intimidating, even for first-time users.

Cold Start vs. Warm Start: Key Differences

The Stihl FS38 uses two distinct starting procedures depending on the engine temperature. Using the wrong procedure for your engine’s state will either cause the engine to fail to start or flood the combustion chamber with excess fuel, requiring extra steps to fix.

When to Use Each Start Method

A cold start is required any time the engine has been off for 30 minutes or more, or if the engine is cool to the touch (below 100°F / 38°C). This is the default starting procedure for most uses, especially after long-term storage or first use of the day. A warm start is used when the engine was recently running (within the last 30 minutes) and is still warm to the touch. This is ideal for quick mid-job restarts, such as when you need to refuel or adjust the cutting line while working.

The table above highlights the key differences between the two procedures. Using the warm start method on a cold engine will almost always fail, as the open choke does not provide enough fuel enrichment to ignite the cold combustion chamber. Conversely, using the cold start method on a warm engine will almost always flood the engine with excess fuel, requiring you to clear the combustion chamber before attempting to restart.

Pre-Start Safety and Preparation Steps

Before you attempt to start your Stihl FS38, completing these quick safety and prep steps will reduce the risk of injury, engine damage, and starting failure:

1. Work in a well-ventilated outdoor area: Never start the trimmer in an enclosed space like a garage or shed, as exhaust fumes contain carbon monoxide, a deadly, odorless gas.
2. Wear appropriate personal protective equipment (PPE): Safety glasses, ear protection, sturdy work gloves, and closed-toe shoes are non-negotiable when operating power equipment.
3. Check the fuel level: Ensure the tank has enough fresh, properly mixed fuel to complete your task. Running out of fuel mid-operation can cause engine damage over time.
4. Inspect the trimmer for damage: Check the cutting line, trimmer head, handle, and starter cord for wear or damage before starting. Do not operate a damaged trimmer.
5. Clear the work area: Remove rocks, sticks, toys, and other debris from the area you’ll be trimming to prevent them from being thrown by the cutting line, which can cause serious injury.
6. Ensure the cutting head is clear and the blade brake is disengaged: Make sure the trimmer line or blade is not touching any objects, and that the blade brake lever is pushed forward to the disengaged position. An engaged brake will prevent the engine from cranking, and a cutting head in contact with debris can cause the engine to stall immediately after starting.

Skipping these prep steps is one of the most common causes of avoidable accidents and starting frustration.

Step-by-Step Cold Start Guide for the Stihl FS38

A cold start is required any time your Stihl FS38 has been off for more than 30 minutes, or if the engine is cool to the touch. Follow these steps exactly to avoid flooding the engine or causing unnecessary wear:

1. Set the choke lever to the closed position: Locate the choke lever on the side of the carburetor (it usually has a “choke” or rabbit icon for closed, and a “run” or turtle icon for open). Slide or rotate the lever fully to the closed position to restrict airflow and enrich the fuel mixture for a cold engine.
2. Press the primer bulb 3–5 times: The primer bulb is the small rubber bulb on the side of the carburetor. Press it firmly with your thumb 3 to 5 times, holding each press for 1–2 seconds to pump fuel from the tank into the carburetor. You should see fuel begin to fill the bulb after 3 presses. If the bulb does not fill, check for fuel line blockages or an empty tank.
3. Squeeze the throttle trigger lock and throttle trigger: Squeeze the lock lever behind the main throttle trigger first, then squeeze the throttle trigger fully. Hold both in the depressed position for the entire starting process. This opens the throttle to allow the correct air-fuel mixture into the engine.
4. Pull the starter cord firmly 2–6 times: Grip the starter handle firmly with one hand, and hold the trimmer steady with the other (place the trimmer head on the ground if needed for stability). Pull the cord smoothly and fully out, then let it retract slowly. Do not yank the cord violently, as this can damage the starter mechanism. You may hear the engine sputter or fire after 2–3 pulls.
5. Move the choke lever to the open position as soon as the engine fires: As soon as you hear the engine try to start or see it sputter, immediately slide the choke lever to the open “run” position. Leaving the choke closed after the engine fires will flood the engine with too much fuel, making it stall or fail to start.
6. Pull the starter cord 1–2 more times to fully start the engine: With the choke open, pull the starter cord 1–2 more times to get the engine running consistently. Once it starts, release the throttle trigger lock and throttle, then let the engine idle for 30 seconds to warm up before applying full throttle or beginning to trim.

If the engine does not start after 6 pulls, release the throttle, wait 10 seconds, and repeat the process. Do not pull the cord more than 6 times in a row without a break, as this can flood the engine.

Step-by-Step Warm Start Guide for the Stihl FS38

A warm start is used when your FS38 has been running recently (within the last 30 minutes) and the engine is still warm. This process is much faster and requires fewer steps than a cold start:

1. Set the choke lever to the fully open position: The choke must be completely open for a warm start, as the warm engine does not need extra fuel enrichment. Leaving the choke closed will flood the engine immediately.
2. Optional: Press the primer bulb 1 time lightly: If the engine sputtered or died when you turned it off, a single light press of the primer bulb can add a small amount of fuel to help it restart. Skip this step if the engine turned off smoothly.
3. Squeeze the throttle trigger lock and throttle trigger fully: Just like with a cold start, hold both levers depressed for the entire starting process to open the throttle.
4. Pull the starter cord 1–2 times: Pull the starter cord smoothly, just as you would for a cold start. The warm engine should start on the first or second pull. Once it starts, release the throttle triggers and let it idle for a few seconds before resuming work.

Warm starts take less than 10 seconds when done correctly, and are ideal for quick mid-job restarts.

Common Starting Issues and Quick Fixes

Even with perfect technique, you may run into starting issues from time to time, especially if your trimmer has been stored for an extended period. The most common problems fall into two categories: fuel system issues and ignition system issues.

Fuel System Problems

Fuel-related issues are the most common cause of starting failure for the Stihl FS38, especially after long-term storage. Common fuel problems include:

• Old or stale fuel: Gasoline degrades after 30 days, and ethanol-blended gas can absorb water, leading to varnish buildup that clogs carburetor jets. Drain old fuel, clean the carburetor, and refill with fresh mix to fix this.
• Incorrect fuel mixture: The FS38 requires a 50:1 fuel-to-oil ratio (2.6 ounces of two-stroke oil per gallon of gasoline). A mixture that is too rich or too lean will prevent starting and can damage the engine. Always use oil designed for air-cooled two-stroke engines.
• Clogged fuel filter: The in-tank fuel filter can clog with debris or varnish, blocking fuel flow. Replace it annually to prevent this issue.
• Flooded engine: Pulling the starter cord too many times with the choke closed, or leaving the choke closed after the engine fires, will flood the combustion chamber with excess fuel. To fix, turn the choke open, remove the spark plug, pull the starter cord 3–4 times to blow out excess fuel, then reinstall the plug and attempt a warm start.

Ignition and Spark Issues

If the fuel system is working but the engine still won’t start, check the ignition system:

• Worn or dirty spark plug: Replace the spark plug every 100 hours of use or annually. A worn electrode or carbon buildup will prevent a strong spark. Clean the plug, check the gap (0.02 inches / 0.5mm), and replace it if damaged.
• Faulty ignition coil: If there is no spark at the plug even when it is clean and properly gapped, the ignition coil may be faulty. This requires a replacement part or professional repair.
• Loose spark plug wire: Ensure the spark plug wire is securely connected to both the plug and ignition coil, as a loose connection will prevent spark.

Best Practices for Reliable Starts Every Time

Following these simple tips will make starting your Stihl FS38 almost effortless, no matter the temperature or how long it’s been since you last used it:

• Use fresh, high-quality fuel: Buy gas from high-volume stations to ensure freshness, and use fuel with no more than 10% ethanol content. Ethanol-free gas is ideal for long-term reliability, as it does not absorb water and reduces varnish buildup.
• Mix fuel in small batches: Only mix enough fuel for 1–2 months of use at a time to prevent stale fuel from clogging the carburetor.
• Store the trimmer correctly: At the end of the season, drain the fuel tank, run the engine until it stalls to clear the carburetor of fuel, and store the trimmer in a cool, dry place to prevent fuel degradation over winter.
• Prime the bulb correctly: For cold starts, press the primer bulb 3–5 times. Do not over-prime (press it more than 5 times), as this will flood the engine with fuel.
• Pull the starter cord smoothly: Yanking the cord violently can damage the starter mechanism. Pull smoothly and fully, then let it retract slowly to avoid wear.
• Warm up the engine before heavy use: Let the engine idle for 30 seconds after starting to allow oil to circulate and reduce internal wear. This also prevents stalling when you engage the throttle for heavy cutting.

Routine Maintenance to Avoid Start Failures

Regular maintenance is the best way to prevent starting issues before they happen. Incorporate these simple checks into your routine to keep your FS38 running reliably:

1. Replace the spark plug annually: A worn spark plug is a top cause of starting failure. Replace it every 100 hours of use or once per year, whichever comes first.
2. Clean or replace the air filter every 25 hours: A clogged air filter restricts airflow to the engine, making starting harder and reducing performance. Clean the air filter with soap and water after each use, and replace it if it is torn or excessively dirty.
3. Replace the fuel filter annually: The in-tank fuel filter prevents debris from reaching the carburetor. Replace it once per year to avoid clogs from varnish or debris.
4. Sharpen or replace the cutting line regularly: A dull cutting line puts extra strain on the engine, making it harder to start and run. Replace the line when it becomes frayed or worn, and sharpen the trimmer blade if your model is equipped with one.
5. Clean the carburetor annually: If you notice the engine idling rough, stalling, or taking more pulls than usual to start, the carburetor may be clogged with varnish. Clean the carburetor jets with a carburetor cleaner spray, or have it professionally cleaned if you are not comfortable doing it yourself.

Frequently Asked Questions

How Many Pulls Should It Take to Cold Start a Stihl FS38?

A properly maintained Stihl FS38 with fresh fuel should start in 2 to 6 pulls when cold. If it takes more than 6 pulls, check that the choke is fully closed, the primer bulb was pressed 3–5 times, the throttle is partially squeezed, and the fuel is fresh. If all of these are correct, you may have a clogged carburetor, worn spark plug, or other ignition issue that needs to be addressed.

Can I Use Stale Fuel in My Stihl FS38?

No, you should never use stale fuel in your Stihl FS38. Gasoline begins to degrade after 30 days, and ethanol-blended gas can absorb water from the air over time, leading to corrosion, varnish buildup, and clogged carburetor jets. Stale fuel is the most common cause of starting failure for gas-powered trimmers that have been stored for more than a few months. Always drain old fuel before long-term storage, and use only fresh fuel for operation.

Why Won’t My FS38 Start After Sitting for Months?

The most common reason a FS38 won’t start after long-term storage is stale fuel that has clogged the carburetor. Other possible causes include a dead spark plug, a disconnected spark plug wire, or a clogged fuel filter. To troubleshoot, first drain the old fuel, clean or replace the spark plug, check the spark plug wire connection, and replace the fuel filter. If the engine still won’t start, the carburetor may need to be professionally cleaned or replaced.

Do I Need to Mix Oil with Gas for My Stihl FS38?

Yes, the Stihl FS38 is a two-stroke engine, which means it requires oil to be mixed directly with the gasoline to lubricate internal moving parts. The correct mixture ratio is 50:1, which is 2.6 ounces of high-quality two-stroke oil (specifically designed for air-cooled engines) per gallon of gasoline. Never use four-stroke engine oil, as it does not have the correct additives for two-stroke engines and will cause carbon buildup and permanent engine damage.

What Type of Gas Is Best for a Stihl FS38?

For best performance and starting reliability, use fresh, unleaded gasoline with an octane rating of 89 or higher, and no more than 10% ethanol content. Ethanol-free gasoline is ideal if available in your area, as it does not absorb water and is less likely to cause varnish buildup in the carburetor. Avoid using gasoline with more than 10% ethanol, as higher ethanol blends can damage the engine’s fuel system over time.

Conclusion

Knowing How to Start a Stihl Fs38 Weed Eater? correctly for both cold and warm conditions is a simple skill that will save you time and frustration every time you need to use your trimmer. The key to reliable starting is following the correct procedure for your engine’s temperature, using fresh properly mixed fuel, and completing regular maintenance to keep the fuel and ignition systems in good shape. By familiarizing yourself with the key components, following the step-by-step guides for cold and warm starts, and addressing common issues quickly, you’ll keep your FS38 running smoothly for years of reliable weed and brush cutting. If you do run into persistent starting problems, don’t hesitate to consult a Stihl authorized service center for professional help to avoid causing further damage to your tool.