Stihl FS 38 Won’t Start (5 Expert Fixes for Quick Revival)
Stihl FS 38 Won’t Start: 5 Expert Fixes for Quick Revival
Before we get started, safety first! Always disconnect the spark plug wire before performing any maintenance on your FS 38. Wear gloves and eye protection. And if you’re uncomfortable with any of these procedures, don’t hesitate to take your trimmer to a qualified service technician.
1. Fuel System Check: The Heart of the Matter
The fuel system is often the culprit when a small engine refuses to start. Think of it like this: your FS 38 needs fuel to breathe life into that engine. Let’s check if it’s getting what it needs.
1.1. Old Fuel: The Silent Saboteur
I cannot stress this enough: old fuel is the enemy. Ethanol-blended gasoline, which is common worldwide, can degrade quickly and absorb moisture. This leads to gumming up the carburetor and fuel lines. I learned this the hard way after letting my FS 38 sit idle over a particularly wet winter. The result? A completely clogged carburetor that required a full rebuild.
- The Fix: Drain the old fuel completely. Use a fuel stabilizer in fresh fuel to prevent degradation. I personally recommend using a fuel stabilizer like Stabil or Sea Foam. If the fuel is visibly discolored or smells stale, it’s definitely time to replace it.
- Technical Tip: Ethanol-free fuel is a great option if you can find it. It’s less likely to cause problems with small engines.
1.2. Fuel Filter: The Gatekeeper
The fuel filter prevents debris from entering the carburetor. A clogged filter restricts fuel flow, leading to starting problems.
- The Fix: Locate the fuel filter inside the fuel tank (it’s attached to the fuel line). Use a small hook or bent wire to carefully pull it out. Inspect it for dirt and debris. If it’s clogged, replace it with a new one.
- Technical Specification: The Stihl FS 38 uses a small, in-tank fuel filter. The pore size is generally around 20-40 microns. This is to filter out fine particles that can damage the carburetor jets.
- DIY Insight: I’ve found that soaking a slightly dirty fuel filter in carburetor cleaner can sometimes restore it, but replacement is always the best option.
1.3. Fuel Lines: The Arteries
Cracked or brittle fuel lines can leak air, disrupting fuel delivery.
- The Fix: Inspect the fuel lines for cracks, kinks, or leaks. Replace any damaged lines.
- Technical Tip: Fuel lines harden and crack over time due to exposure to fuel and UV radiation. Replace them preventatively every 2-3 years, especially if you live in a climate with extreme temperatures.
- Material Specification: Fuel lines for the FS 38 are typically made of a fuel-resistant synthetic rubber or plastic. The inner diameter is usually around 3/32″ or 2.5mm.
1.4. Carburetor: The Fuel Mixer
The carburetor mixes fuel and air in the correct proportions for combustion. A clogged carburetor is a common cause of starting problems. This is where my experience with old fuel really comes into play.
- The Fix:
- Carburetor Cleaner: Spray carburetor cleaner into the carburetor throat while attempting to start the engine. This might dislodge some debris.
- Carburetor Rebuild: If cleaning doesn’t work, you may need to rebuild the carburetor. This involves disassembling the carburetor, cleaning all the parts, and replacing any worn or damaged components. Carburetor rebuild kits are readily available.
- Technical Details: The carburetor on the FS 38 is a simple, non-adjustable carburetor. It relies on fixed jets to meter the fuel. This means that cleaning the jets is crucial for proper operation.
- Case Study: I once worked on a Stihl FS 38 that had been sitting unused for several years. The carburetor was completely gummed up with old fuel residue. I disassembled the carburetor, soaked all the parts in carburetor cleaner for several hours, and then carefully cleaned each jet with a fine wire. After reassembling the carburetor, the trimmer started on the first pull.
- Important Note: If you’re not comfortable rebuilding a carburetor, take it to a professional. Incorrect reassembly can damage the engine.
2. Ignition System Check: Spark of Life
The ignition system provides the spark that ignites the fuel-air mixture. No spark, no start.
2.1. Spark Plug: The Igniter
A fouled or damaged spark plug can prevent the engine from starting.
- The Fix: Remove the spark plug and inspect it. Clean it with a wire brush or replace it if it’s heavily fouled, cracked, or damaged. Check the spark gap using a spark plug gapping tool. The correct gap for the FS 38 is typically 0.5mm (0.020 inches).
- Technical Specification: The spark plug for the FS 38 is typically a Bosch WSR6F or NGK BPM7A.
- Pro Tip: When reinstalling the spark plug, tighten it to the correct torque specification (typically around 15-20 Nm or 11-15 ft-lbs). Over-tightening can damage the cylinder head.
- Visual Example: Compare a clean spark plug to a fouled one. Fouled plugs will often be black and oily or covered in carbon deposits.
2.2. Spark Plug Wire and Boot: The Conductors
A damaged spark plug wire or boot can prevent the spark from reaching the spark plug.
- The Fix: Inspect the spark plug wire and boot for cracks, cuts, or loose connections. Replace any damaged components. Ensure the boot is securely attached to the spark plug.
- Safety Note: Always disconnect the spark plug wire from the spark plug before inspecting the wire and boot.
2.3. Ignition Coil: The Spark Generator
The ignition coil generates the high-voltage spark needed to ignite the fuel-air mixture. A faulty ignition coil can prevent the engine from starting.
- The Fix: Testing the ignition coil requires a multimeter. Disconnect the spark plug wire and set the multimeter to measure resistance. Measure the resistance between the spark plug wire terminal and the engine ground. Consult the service manual for the correct resistance range. If the resistance is outside the specified range, the ignition coil may be faulty and needs to be replaced.
- Technical Details: The ignition coil on the FS 38 is a solid-state electronic ignition system. This system is generally reliable, but it can fail due to heat or vibration.
- Important Note: Testing the ignition coil can be dangerous. If you’re not comfortable with electrical testing, take your trimmer to a professional.
3. Air Intake Check: Breathing Easy
The engine needs air to run. A blocked air filter or air intake can prevent the engine from starting.
3.1. Air Filter: The Protector
The air filter prevents dirt and debris from entering the engine. A clogged air filter restricts airflow, leading to starting problems.
- The Fix: Remove the air filter and inspect it. Clean it with compressed air or replace it if it’s heavily soiled.
- Technical Specification: The air filter for the FS 38 is typically a foam filter. It should be cleaned regularly to maintain optimal engine performance.
- Maintenance Tip: I like to wash my foam air filters in warm, soapy water and then let them air dry completely before reinstalling them. Oiling the air filter lightly with air filter oil after cleaning can improve its filtering efficiency.
3.2. Air Intake: The Pathway
Make sure nothing is blocking the air intake. Leaves, debris, or even spiderwebs can obstruct the airflow.
- The Fix: Inspect the air intake for any obstructions. Remove any debris that you find.
4. Compression Check: The Power Within
The engine needs compression to run. Low compression can prevent the engine from starting.
4.1. Compression Test: The Verdict
A compression test measures the pressure inside the cylinder. Low compression indicates a problem with the piston rings, cylinder walls, or valves (although valves are not present on the FS 38, as it is a 2-stroke engine).
- The Fix: Performing a compression test requires a compression tester. Remove the spark plug and screw the compression tester into the spark plug hole. Pull the starter rope several times and note the reading on the compression tester. Consult the service manual for the correct compression range.
- Technical Details: The compression ratio for the FS 38 is typically around 9:1. A healthy engine should have a compression reading of at least 100 PSI.
- Important Note: A compression test can be a good indicator of engine health, but it’s not always definitive. Other factors, such as a leaky crankshaft seal, can also cause low compression.
- DIY Insight: I once worked on an FS 38 that had low compression. After disassembling the engine, I found that the piston rings were worn and the cylinder walls were scored. Replacing the piston and cylinder restored the engine’s compression and power.
5. Starter Mechanism Check: The Initial Push
The starter mechanism engages the engine and allows you to pull the starter rope. A faulty starter mechanism can prevent the engine from starting.
5.1. Starter Rope and Recoil Spring: The Pull
Inspect the starter rope for fraying or breakage. Check the recoil spring to make sure it’s working properly.
- The Fix: Replace the starter rope if it’s frayed or broken. Replace the recoil spring if it’s weak or broken.
- Technical Tip: When replacing the starter rope, use a rope that is the correct diameter and length. Too thick or too short a rope can cause problems.
- DIY Insight: I once had a recoil spring break on my FS 38. Replacing the spring was a relatively simple job, but it required disassembling the starter mechanism. Be careful when disassembling the starter mechanism, as the recoil spring can be under tension and can cause injury if released suddenly.
5.2. Starter Pawls: The Engagement
The starter pawls engage with the flywheel to turn the engine over. If the pawls are worn or damaged, they may not engage properly.
- The Fix: Inspect the starter pawls for wear or damage. Replace them if necessary.
- Technical Details: The starter pawls are small, spring-loaded levers that pivot to engage with the flywheel. Over time, the pawls can wear down or the springs can weaken, causing them to not engage properly.
Conclusion: Back to Work!
Troubleshooting a small engine can be frustrating, but with a systematic approach and a little patience, you can usually get it running again. I’ve found that the key is to start with the simplest things first and then work your way up to the more complex issues. Remember to always prioritize safety and don’t hesitate to seek professional help if you’re uncomfortable with any of these procedures. Now, get back out there and tackle that yard work! And remember, a little preventative maintenance can go a long way in keeping your Stihl FS 38 running smoothly for years to come.
