Stihl 250 Carburetor Fixes (5 Expert Tips)

Ever felt like your Stihl 250 chainsaw is just not pulling its weight? Like it’s coughing and sputtering more than actually cutting? Let me guess, you’re thinking it’s time for a new saw. Hold on a second! Before you shell out your hard-earned cash, let’s dive into some carburetor fixes. I’ve spent years troubleshooting these issues, and trust me, nine times out of ten, it’s something you can tackle yourself.

Stihl 250 Carburetor Fixes: 5 Expert Tips to Get Your Saw Humming

Over the years, I’ve seen countless Stihl 250s come into my shop with similar issues. From hobbyists cutting firewood for winter to small-scale loggers felling trees for a living, the Stihl 250 is a reliable workhorse, but even the best machines need some TLC. These five tips are born from my own experiences, research, and countless hours spent tinkering with these carburetors. I’ve distilled the essential knowledge you need to diagnose and fix common problems. Let’s get started!

1. The Initial Assessment: Is It Really the Carburetor?

Before we even think about touching the carburetor, we need to make sure that’s actually the problem. I’ve seen folks tear apart their carburetors only to find out the issue was a clogged fuel filter or a bad spark plug. Don’t be that person!

Fuel System Check: Start by inspecting the fuel lines for cracks or leaks. A common issue is the fuel line hardening and cracking with age, especially with ethanol-blended fuels. Replace them if you find any damage. Next, check the fuel filter inside the fuel tank. A clogged filter restricts fuel flow and starves the engine. Replace it if it’s dirty or clogged. I recommend replacing the fuel filter annually, regardless of its appearance. Fuel filters are cheap insurance against fuel starvation issues.
Spark Plug Inspection: Remove the spark plug and inspect it. Is it wet, dry, black, or tan? A black, sooty plug indicates a rich fuel mixture (too much fuel), while a white or light tan plug indicates a lean mixture (not enough fuel). A wet plug could indicate flooding. A healthy plug should be a light tan color. Clean or replace the spark plug as needed. Check the spark gap using a feeler gauge. The correct spark gap for a Stihl 250 is typically around 0.020 inches (0.5 mm).
Air Filter Inspection: A dirty air filter restricts airflow, causing a rich fuel mixture. Remove the air filter and inspect it. Clean it with soap and water, or replace it if it’s heavily soiled. I’ve found that using compressed air to clean foam filters can damage them over time, so I prefer washing them gently.
Exhaust System Check: A clogged spark arrestor screen can also cause running issues. Remove the spark arrestor screen from the muffler and inspect it. Clean it with a wire brush if it’s clogged with carbon deposits.

Data Point: I once worked on a Stihl 250 that was exhibiting classic carburetor symptoms: rough idling and stalling. After meticulously cleaning the carburetor, the problem persisted. It turned out the exhaust port on the cylinder was partially blocked with carbon buildup, restricting exhaust flow. This highlights the importance of a thorough initial assessment.

2. The Carburetor Cleaning Crusade: Getting Down and Dirty

Okay, so you’ve ruled out the other suspects, and you’re confident the carburetor is the culprit. Time to get your hands dirty! Before you start, remember to work in a clean, well-lit area. Small carburetor parts are easily lost.

Disassembly: Carefully disassemble the carburetor, taking pictures as you go. This will help you remember how everything goes back together. Pay close attention to the orientation of the diaphragms and gaskets.
Cleaning: The key to a successful carburetor cleaning is using the right cleaning solution. I recommend using a dedicated carburetor cleaner. Avoid using harsh chemicals like brake cleaner, as they can damage the rubber and plastic components. Soak the carburetor body and parts in the cleaner for at least 30 minutes. For stubborn deposits, use a soft-bristled brush or carburetor cleaning needles to gently scrub away the grime. Pay special attention to the tiny passages and jets. I’ve found that using a strand of copper wire can be helpful for clearing out clogged jets, but be careful not to enlarge the orifice.
Compressed Air: After soaking and scrubbing, use compressed air to blow out all the passages and jets. Make sure you wear eye protection!
Reassembly: Reassemble the carburetor, referring to the pictures you took during disassembly. Replace any worn or damaged parts, such as diaphragms, gaskets, and needles. Carburetor rebuild kits are readily available and relatively inexpensive.

Personal Story: Years ago, I was helping a friend clear some brush after a storm. His Stihl 250 was running terribly. We took the carburetor apart, and it was filthy. After a thorough cleaning, the saw ran like new. He was amazed at the difference. That experience solidified my belief in the power of a good carburetor cleaning.

3. The Art of Adjustment: Fine-Tuning for Peak Performance

Once the carburetor is clean and reassembled, it’s time to adjust it. The Stihl 250 carburetor typically has two adjustment screws: the “H” screw (high-speed) and the “L” screw (low-speed). These screws control the fuel mixture at different engine speeds.

Initial Settings: Start by setting both the “H” and “L” screws to their initial settings. These settings vary depending on the carburetor model, but a common starting point is 1 turn out from fully closed for both screws. Consult your Stihl 250 owner’s manual for the specific initial settings for your carburetor.
Idle Speed Adjustment: Start the saw and let it warm up for a few minutes. Adjust the idle speed screw (usually marked “LA”) until the chain stops moving at idle.
Low-Speed Adjustment: Adjust the “L” screw until the engine idles smoothly and accelerates cleanly without hesitation. If the engine stalls or hesitates when you open the throttle, the mixture is too lean. Turn the “L” screw out (counterclockwise) slightly to richen the mixture. If the engine bogs down or smokes excessively, the mixture is too rich. Turn the “L” screw in (clockwise) slightly to lean the mixture.
High-Speed Adjustment: Adjust the “H” screw for maximum power at high speed. This is best done with the saw cutting wood. If the engine bogs down or sounds like it’s four-stroking (a burbling sound), the mixture is too rich. Turn the “H” screw in (clockwise) slightly to lean the mixture. If the engine screams or sounds like it’s two-stroking (a high-pitched whine), the mixture is too lean. Turn the “H” screw out (counterclockwise) slightly to richen the mixture. Important: Running the engine too lean at high speed can cause serious engine damage. Be careful not to lean the mixture too much.

Safety Code Consideration: When adjusting the high-speed screw, be mindful of the engine’s operating temperature. Running the engine too lean can cause it to overheat, which can lead to premature wear or even engine failure. Always err on the side of caution and keep the mixture slightly rich.

Unique Insight: I’ve noticed that the ideal carburetor settings can vary depending on altitude and temperature. At higher altitudes, the air is thinner, so you may need to lean the mixture slightly. In colder weather, you may need to richen the mixture slightly.

4. The Ethanol Enigma: Fuel Considerations for Longevity

Ethanol-blended fuels can wreak havoc on small engines, including the Stihl 250. Ethanol absorbs water, which can lead to corrosion and fuel system problems.

Fuel Stabilizer: Always use a fuel stabilizer in your fuel mixture to prevent ethanol-related problems. I recommend using a fuel stabilizer specifically designed for small engines.
Avoid E85: Never use E85 fuel in your Stihl 250. E85 contains a much higher concentration of ethanol (up to 85%) and can damage the engine.
Fresh Fuel: Use fresh fuel. Ethanol-blended fuel can degrade quickly, especially if it’s stored for long periods. I recommend using fuel that’s no more than 30 days old.
Drain Fuel: If you’re not going to use your Stihl 250 for an extended period, drain the fuel tank and run the engine until it stalls to empty the carburetor. This will prevent fuel from gumming up the carburetor.

Data-Backed Content: A study by the Outdoor Power Equipment Institute (OPEI) found that ethanol-blended fuels can cause significant damage to small engines, including fuel system corrosion, carburetor problems, and engine failure. The study recommended using fuel with no more than 10% ethanol (E10) and using a fuel stabilizer.

Tool Requirement: A fuel tester can be used to check the ethanol content of your fuel. These testers are relatively inexpensive and can help you avoid using fuel with too much ethanol.

5. The Beyond-the-Carburetor Conundrum: When to Seek Professional Help

Sometimes, despite your best efforts, the carburetor just can’t be fixed. Or, the problem might not be the carburetor at all. Here are some signs that it’s time to seek professional help:

Persistent Problems: If you’ve cleaned and adjusted the carburetor multiple times and the saw still isn’t running right, there may be a more serious problem.
Engine Damage: If you suspect internal engine damage, such as a scored piston or cylinder, it’s best to take the saw to a qualified technician.
Specialized Tools: Some carburetor repairs require specialized tools, such as a carburetor flow meter. If you don’t have these tools, it’s best to leave the repair to a professional.
Complex Carburetors: Some Stihl 250 models have more complex carburetors with multiple adjustments and features. If you’re not comfortable working on these carburetors, it’s best to seek professional help.

Case Study: I had a customer bring in a Stihl 250 that was running very poorly. He had already tried cleaning and adjusting the carburetor himself, but the problem persisted. After inspecting the saw, I discovered that the cylinder was scored due to a lack of lubrication. The saw needed a complete engine rebuild, which was beyond the scope of what the customer could do himself.

Technical Limitations: Keep in mind that there are limitations to what you can do yourself. Some carburetor problems, such as a warped carburetor body or a damaged throttle shaft, require specialized tools and expertise to repair. Don’t be afraid to seek professional help when needed.

Bonus Tip: Wood Selection Criteria and Tool Calibration Standards

While we’re talking about Stihl 250s and getting the most out of them, let’s briefly touch on wood selection and tool calibration, as these factors directly impact the saw’s performance and longevity.

Wood Selection Criteria: Understanding the type of wood you’re cutting is crucial. Hardwoods like oak and maple require more power and can put more strain on the saw than softwoods like pine and fir. Always use the appropriate chain and bar for the type of wood you’re cutting. For hardwoods, I recommend using a chain with a lower profile and a narrower kerf to reduce the amount of power required.
- Data Point: Oak has a Janka hardness rating of around 1,290 lbf (pounds-force), while pine has a Janka hardness rating of around 380 lbf. This means that oak is significantly harder and requires more force to cut.
Tool Calibration Standards: Regularly calibrating your chainsaw is essential for safe and efficient operation. This includes checking the chain tension, bar alignment, and carburetor settings. A properly calibrated chainsaw will cut more smoothly, reduce the risk of kickback, and prolong the life of the saw.
- Practical Tip: Use a chain tension gauge to ensure that the chain is properly tensioned. The chain should be snug against the bar but still able to be pulled around by hand.

Firewood Preparation and Technical Requirements

Now, let’s get down to the nitty-gritty of firewood preparation. Knowing the technical requirements is essential for producing high-quality firewood that burns efficiently and safely.

Log Dimensions: The ideal log dimensions for firewood vary depending on the size of your wood stove or fireplace. A common length is 16 inches, but you may need to adjust this depending on your specific needs. The diameter of the logs should also be appropriate for your stove or fireplace.
- Precise Measurement: A cord of firewood is defined as a stack of wood that is 4 feet high, 4 feet wide, and 8 feet long, or 128 cubic feet.
Wood Moisture Content: The moisture content of firewood is crucial for efficient burning. Green wood contains a lot of water, which makes it difficult to ignite and burns inefficiently. Seasoned wood, on the other hand, has a lower moisture content and burns hotter and cleaner.
- Material Specification: The ideal moisture content for firewood is between 15% and 20%. You can measure the moisture content of wood using a moisture meter.
- Drying Tolerances: The drying time for firewood varies depending on the type of wood, the climate, and the storage conditions. Hardwoods typically take longer to season than softwoods. As a general rule, firewood should be seasoned for at least six months before burning.
Safety Equipment Requirements: When preparing firewood, always wear appropriate safety equipment, including safety glasses, hearing protection, gloves, and steel-toed boots. A chainsaw chaps are also essential for protecting your legs from accidental cuts.
Cutting Patterns: Use safe and efficient cutting patterns when bucking logs into firewood. Avoid cutting logs that are lying on the ground, as this can increase the risk of kickback. Use a sawhorse to support the logs while you’re cutting them.

By following these expert tips, you can keep your Stihl 250 running smoothly and efficiently for years to come. Remember to always prioritize safety and seek professional help when needed. Happy cutting!

Stihl 250 Carburetor Fixes (5 Expert Tips)