How to Start a Stihl Weed Eater Fs45? Easy Starting Steps

Introduction

The Stihl FS45 is a lightweight, gas-powered string trimmer beloved by homeowners and landscaping professionals for its durability and ease of use when running properly. However, its 2-stroke engine requires a specific starting procedure that many new owners find confusing, especially if the trimmer has been sitting unused for weeks or months. Incorrect starting steps can lead to a flooded engine, hard starting, or even permanent engine damage if you use the wrong fuel. This comprehensive guide walks you through every step of starting your FS45, from pre-start safety checks to troubleshooting common issues, so you can spend less time fighting with your trimmer and more time getting work done. Whether you’re a first-time FS45 owner or just need a refresher on the correct starting process, this guide covers everything you need to know to master how to start a Stihl Weed Eater Fs45? quickly and safely.

• Introduction
• Understanding Your Stihl FS45 Weed Eater
• Pre-Start Safety Checks
• Fueling Your FS45: The Right Mix Matters
• Step-by-Step Cold Start Guide for the FS45
• Step-by-Step Warm Start Guide for the FS45
• Troubleshooting Common Starting Issues
• Post-Start Maintenance and Best Practices
• Common Mistakes to Avoid When Starting Your FS45
• Frequently Asked Questions
• Conclusion

Understanding Your Stihl FS45 Weed Eater

The FS45 is powered by a 1.5-horsepower 2-stroke engine, which is lighter and more powerful than comparable 4-stroke trimmers, making it ideal for edging sidewalks, trimming overgrown weeds, and clearing light brush around your property. Unlike electric trimmers, it doesn’t require a cord or battery, giving you unlimited runtime as long as you have fuel on hand. Understanding the key components of your FS45 will make the starting process far less intimidating, as you’ll know exactly what each part does and why it’s important for getting the engine running.

Key Components of the FS45

Familiarize yourself with these core parts before attempting to start the trimmer:

• Primer bulb: A small rubber bulb located near the carburetor that pumps fuel from the tank to the carburetor to help with cold starts. Pressing it multiple times fills the carburetor with fuel so the engine can turn over without excessive pulling.
• Choke lever: A small lever on the side of the engine that restricts air flow to enrich the fuel mixture for cold engines. It has two positions: closed (cold start) and open (run/warm start).
• Throttle trigger and lock: The trigger controls engine speed, and the small lock lever next to it holds the throttle in the partially open start position, which gives the engine the extra air and fuel it needs to turn over when starting.
• Starter rope: A manual pull cord that turns the engine over to start it. Pull it firmly and quickly for best results.
• Fuel shutoff valve: A small valve on the fuel tank that stops fuel flow to the carburetor to prevent leaks when the trimmer is stored or transported. It must be turned to the “on” position before starting.
• Air filter: A foam or paper filter that prevents grass, dust, and debris from entering the engine. A dirty air filter will restrict air flow and make starting difficult.
• Spark plug: A small component that creates a spark to ignite the fuel mixture in the engine. A fouled or worn spark plug is a common cause of starting issues.

Pre-Start Safety Checks

Before you even think about pulling the starter rope, completing a quick safety check will prevent injury and damage to your trimmer. First, clear the work area of rocks, sticks, toys, and other debris that could be thrown by the cutting attachment at high speed. Wear proper personal protective equipment: cut-resistant gloves, safety glasses or goggles, long pants, and closed-toe shoes. Never wear sandals or shorts when operating the FS45, as the cutting line can throw debris or cause serious cuts.

Inspect the trimmer for visible damage: check the fuel lines for cracks, the cutting attachment for dullness or damage, and make sure the guard is securely attached to the bottom of the cutting attachment. A loose guard can fly off during operation and cause serious injury. If you notice any cracks in the fuel lines or a strong smell of gas when you pick up the trimmer, do not attempt to start it until you have the leaks repaired. Finally, disconnect the spark plug wire if you’re inspecting the cutting attachment to avoid accidental starting.

Fueling Your FS45: The Right Mix Matters

The Stihl FS45 uses a 2-stroke engine, which requires a premixed blend of gasoline and 2-stroke oil to run properly. Using the wrong fuel mix is the most common cause of starting issues and permanent engine damage, so this step is critical. Unlike 4-stroke engines that have a separate oil reservoir, 2-stroke engines get their lubrication from the oil mixed directly into the fuel.

Step-by-Step Fuel Mixing Guide

Follow these steps to mix the correct fuel for your FS45:

1. Use only fresh, unleaded gasoline with an octane rating of 89 or higher. Avoid fuel with more than 10% ethanol, as ethanol breaks down quickly and can clog the carburetor over time.
2. Use only Stihl-approved 2-stroke oil, which is formulated for high performance and maximum engine protection. Never use automotive oil, as it lacks the necessary additives for 2-stroke engines and will cause premature wear.
3. Mix fuel in a clean, approved fuel container: for the required 50:1 ratio, add 2.6 fluid ounces of oil to 1 gallon of gas. For smaller batches, use 0.8 fluid ounces of oil per 1 quart of gas.
4. Shake the container thoroughly for 10 to 15 seconds to mix the oil and gas completely before filling the FS45’s fuel tank. Never mix fuel directly in the trimmer’s tank, as it can lead to an inconsistent mix.

Stihl also sells pre-mixed fuel that is already blended at the correct 50:1 ratio, which is a convenient option for users who don’t want to mix their own fuel, especially for occasional use.

Cold vs. Warm Weather Fuel Adjustments

Temperature can affect how your fuel performs, so make small adjustments for extreme weather. In temperatures below 40°F (4°C), use a winter-grade 2-stroke oil to prevent the fuel from gelling and clogging the carburetor. You can also add a fuel stabilizer to prevent the fuel from breaking down in cold conditions. In warm weather above 80°F (27°C), standard Stihl 2-stroke oil works fine, but avoid over-oiling the mix, as this can cause carbon buildup on the spark plug and make starting harder.

Step-by-Step Guide: How to Start a Stihl Weed Eater Fs45? (Cold Start)

A cold start is required when the FS45 has been sitting for more than 30 minutes, or the engine is at room temperature or cooler. Follow these steps exactly to avoid flooding the engine or causing unnecessary wear:

1. Place the FS45 on a flat, stable surface. Ensure the cutting attachment is clear of grass, rocks, and other obstacles to prevent damage when the engine starts.
2. Turn the fuel shutoff valve (located on the fuel tank) to the “on” position. This allows fuel to flow from the tank to the carburetor.
3. Press the primer bulb (located near the carburetor, on the side of the engine) 6 to 8 times. You will see fuel begin to fill the bulb; stop pressing once the bulb is firm and full of fuel. This primes the carburetor with fuel so the engine can start without excessive pulling.
4. Move the choke lever (located on the side of the engine, near the air filter) to the fully closed “cold start” position. This enriches the fuel mixture by restricting air flow, which is necessary for a cold engine that can’t vaporize fuel efficiently.
5. Press the throttle trigger halfway, then engage the throttle lock (a small lever next to the trigger) to hold the throttle in the partially open start position. This gives the engine the extra air and fuel it needs to turn over.
6. Pull the starter rope slowly 2 to 3 times to let the engine turn over and draw fuel into the combustion chamber. Then pull the rope firmly and quickly 3 to 5 times. You will hear the engine sputter or fire briefly, but it will not run continuously yet.
7. As soon as you hear the engine sputter, move the choke lever immediately to the fully open “run” position. If you leave the choke closed, the engine will flood with too much fuel and die.
8. Press the throttle trigger slightly to keep the engine running, and let it idle for 30 seconds to warm up. Do not use full throttle until the engine has warmed up completely.
9. If the engine dies during warm-up, repeat steps 3 through 8, making sure the primer bulb is fully pressed and the choke is moved to the run position as soon as the engine sputters. If the engine doesn’t start after 5 pulls, wait 30 seconds before trying again to avoid flooding.

Step-by-Step Guide: How to Start a Stihl Weed Eater Fs45? (Warm Start)

If you’ve been using the FS45 recently and the engine is still warm, you can skip the choke and reduce the number of primer bulb presses to start it faster. A warm engine already has vaporized fuel in the combustion chamber, so it doesn’t need the enriched fuel mix provided by the choke. Follow these steps for a quick warm start:

1. Place the FS45 on a flat surface, clear of obstacles.
2. Turn the fuel shutoff valve to the “on” position.
3. Press the primer bulb only 2 to 3 times. Over-priming a warm engine will flood it with fuel, making starting impossible until the excess fuel evaporates.
4. Leave the choke lever in the fully open “run” position. A warm engine does not need the enriched fuel mixture provided by the choke.
5. Pull the starter rope firmly and quickly 1 to 2 times. The engine should start immediately.
6. Let the engine idle for 10 to 15 seconds before applying full throttle to avoid putting unnecessary strain on the engine.

Troubleshooting Common Starting Issues

Even with the correct steps, you may run into starting issues from time to time, especially if the FS45 has been stored improperly or needs basic maintenance. Most starting problems are easy to fix with basic tools and a little know-how. Below is a comparison table of the most common FS45 starting problems, their likely causes, and quick fixes to get you back up and running.

Common FS45 Starting Problems and Fixes

If you’ve tried all the fixes in the table and the FS45 still won’t start, you may have a more serious issue with the carburetor or ignition system. In this case, take the trimmer to a Stihl authorized service center for professional diagnosis and repair.

Post-Start Maintenance and Best Practices

Once your FS45 is running, following a few simple best practices will extend its lifespan and keep it performing well for years. First, let the engine idle for 30 seconds after a cold start, or 10 seconds after a warm start, before applying full throttle. This allows the oil to circulate through the engine and lubricate all moving parts, preventing premature wear.

After each use, clean the air filter with warm soapy water, let it dry completely, and reinstall it to prevent debris from entering the engine. Check the cutting attachment for dullness or damage after each use, and sharpen or replace it as needed to maintain cutting efficiency. Wipe down the engine with a clean cloth to remove grass and debris, which can trap moisture and cause corrosion. Check the trimmer line regularly, and replace it when it gets down to 6 inches or less to maintain cutting performance.

If you plan to store the FS45 for more than 30 days, drain all fuel from the tank and carburetor to prevent stale fuel from clogging the system. Stale fuel is the top cause of long-term starting issues, so this step is critical for off-season storage. Store the trimmer in a cool, dry place, out of direct sunlight, and hang it up to avoid damage to the fuel lines.

Common Mistakes to Avoid When Starting Your FS45

Many FS45 starting issues are caused by simple, avoidable mistakes. Knowing what not to do will save you time, frustration, and costly repairs. Avoid these common errors:

• Using old or ethanol-heavy fuel: Gasoline with more than 10% ethanol breaks down within 30 days, clogging the carburetor and causing starting issues. Always use fresh fuel, and add a fuel stabilizer if you won’t use the fuel within a month. If you must use ethanol-containing fuel, choose fuel with no more than 10% ethanol.
• Over-priming the carburetor: Pressing the primer bulb too many times, especially on a warm engine, will flood the engine with fuel. Stick to the recommended 6-8 presses for cold starts and 2-3 for warm starts. If you press the primer bulb and no fuel fills the bulb, check that the fuel shutoff is on and the fuel tank has gas.
• Using the wrong fuel mix ratio: Never use straight gas, or mix oil at the wrong ratio. The FS45 requires a precise 50:1 gas-to-oil mix; using too little oil will damage the engine, and too much oil will cause carbon buildup and hard starting. Never use automotive oil in your 2-stroke engine, as it lacks the necessary lubricating additives.
• Forcing the starter rope: If the rope is hard to pull, never yank it forcefully. This can break the starter mechanism or bend the crankshaft. First, disconnect the spark plug wire, check for jams in the cutting attachment, and make sure the engine isn’t locked from lack of oil.
• Skipping pre-start safety checks: Failing to clear the work area or wear PPE can lead to serious injury from debris thrown by the cutting attachment, or cuts from the trimmer line.
• Storing the FS45 with full fuel: Stale fuel is the top cause of long-term starting issues. Always drain the fuel tank and carburetor before storing the trimmer for more than 30 days to prevent fuel from breaking down and clogging the system.

Frequently Asked Questions

Why won’t my Stihl FS45 start after sitting for months?

If it’s been stored for more than 30 days, the fuel in the carburetor has likely gone stale and clogged the fuel passages. Drain the old fuel, mix fresh 50:1 fuel, press the primer bulb fully, and follow the cold start steps. You can also try spraying a small amount of starting fluid directly into the carburetor air intake to help get the engine running if stale fuel is the issue, but this is only a temporary fix. You will still need to clean the carburetor and replace the fuel to prevent the issue from recurring. If it still won’t start, you may need to clean the carburetor or replace the spark plug.

What fuel mix ratio does the Stihl FS45 require?

The FS45 uses a 50:1 fuel-to-oil ratio, meaning 1 gallon of fresh, unleaded 89+ octane gas mixed with 2.6 fluid ounces of Stihl-approved 2-stroke oil. Never use automotive oil or ethanol-heavy fuel (more than 10% ethanol) as it can damage the engine. Using a mix that is too rich (too much oil) will cause the engine to smoke heavily and run poorly, while a mix that is too lean (too little oil) will cause overheating and premature engine wear.

How many times should I press the primer bulb when starting?

For cold starts (engine at room temperature or cooler), press the primer bulb 6-8 times until you see fuel in the bulb. For warm starts, only press it 2-3 times. Over-priming will flood the engine and make starting harder. If you press the primer bulb and no fuel fills the bulb, check that the fuel shutoff is on and the fuel tank has gas. If the bulb still doesn’t fill, there may be a clog in the fuel line that needs to be cleared.

Can I use ethanol-free gas in my FS45?

Yes, ethanol-free gas is actually recommended for the FS45, as ethanol can break down over time and clog the carburetor. If you can’t find ethanol-free fuel, use a fuel stabilizer with every fill to extend the life of the fuel and prevent clogs. If you must use ethanol-containing fuel, choose fuel with no more than 10% ethanol, and add a fuel stabilizer at every fill to prevent the ethanol from breaking down and damaging the carburetor.

How often should I replace the spark plug on my FS45?

Stihl recommends replacing the spark plug every 100 hours of use, or once per year if you use the trimmer less frequently. A fouled or worn spark plug will cause starting issues and poor performance, so check it regularly if you have trouble starting. A fouled spark plug will have a black, sooty coating on the electrode, which prevents it from creating a spark. You can clean it with a wire brush, but if the electrode is worn or damaged, replace the spark plug for best performance.

Conclusion

Mastering how to start a Stihl Weed Eater Fs45? is far simpler than it seems once you understand the basic steps and avoid common pitfalls. Whether you’re performing a cold start after months of storage or a quick warm start mid-job, following the correct fueling, priming, and choke procedures will get your trimmer running in seconds. Remember to always complete pre-start safety checks, use the correct 50:1 fuel mix, and avoid over-priming or forcing the starter rope. With regular maintenance and proper storage, your FS45 will stay reliable for years of weed trimming and light brush clearing. If you do run into starting issues, refer to the troubleshooting table above to diagnose and fix the problem quickly, no professional help needed. With these tips, you’ll spend less time troubleshooting and more time keeping your yard looking its best.