Stihl MS 250 Carburetor Adjustment (Easy Tune-Up Tips For Firewood)

Isn’t it funny how sometimes the very thing that gives us warmth and comfort – a roaring fire built with neatly stacked firewood – can be a real pain to get started? Especially when your chainsaw, the trusty workhorse that helps create that firewood, is acting up. A poorly tuned chainsaw is like a grumpy woodcutter: inefficient, unreliable, and prone to giving you headaches. That’s why understanding how to adjust the carburetor on your Stihl MS 250 is absolutely crucial, especially if you’re aiming for an efficient and productive firewood season.

Stihl MS 250 Carburetor Adjustment: Easy Tune-Up Tips for Firewood

Understanding the User Intent

The user’s intent is clear: they want a practical, easy-to-understand guide on how to adjust the carburetor on their Stihl MS 250 chainsaw, specifically for firewood preparation. They are likely experiencing issues with their chainsaw’s performance, such as difficulty starting, poor idling, or lack of power when cutting. They want to learn how to troubleshoot these issues and fine-tune their chainsaw for optimal performance in firewood-related tasks. The “Easy Tune-Up Tips” aspect suggests a desire for simplified instructions and practical advice.

Why Carburetor Adjustment Matters for Firewood

The carburetor is the heart of your Stihl MS 250, responsible for mixing air and fuel in the correct proportions to create a combustible mixture. When this mixture is off, your chainsaw will not run efficiently. For firewood preparation, this can mean:

Hard starting: Wasting time and energy just trying to get the saw going.
Poor idling: The saw stalls frequently, interrupting your work.
Lack of power: Slow and inefficient cutting, requiring more effort and time.
Excessive fuel consumption: Burning through more fuel than necessary, increasing costs.
Increased emissions: Contributing to air pollution.
Engine damage: Running too lean or too rich can damage the engine over time.

Think of it like this: imagine trying to run a marathon with a clogged airway. You might make it, but it will be a struggle, and you won’t be performing at your best. A properly tuned carburetor ensures your chainsaw runs smoothly and efficiently, making firewood preparation a much more enjoyable and productive experience.

Key Terms and Concepts

Before diving into the adjustment process, let’s define some essential terms:

Carburetor: A device that mixes air and fuel for internal combustion engines.
Air/Fuel Mixture: The ratio of air to fuel in the combustion chamber.
Lean Mixture: Too much air, not enough fuel. Can cause overheating and engine damage.
Rich Mixture: Too much fuel, not enough air. Can cause poor performance, excessive smoke, and fouled spark plugs.
Idle Speed: The engine’s speed when not engaged in cutting.
High-Speed Jet (H): Controls fuel flow at high engine speeds (during cutting).
Low-Speed Jet (L): Controls fuel flow at low engine speeds (idling and initial acceleration).
Idle Speed Screw (LA/T): Controls the throttle plate opening at idle, adjusting the idle speed.
RPM (Revolutions Per Minute): A measure of engine speed.
Tachometer: A device used to measure engine RPM.
Green Wood: Freshly cut wood with high moisture content.
Seasoned Wood: Wood that has been dried to reduce moisture content, making it ideal for burning.

Tools and Materials You’ll Need

Screwdriver: A small, flat-head screwdriver is essential for adjusting the carburetor screws. Stihl often provides a specialized tool for this, but a standard screwdriver will work.
Tachometer (Optional but Recommended): A tachometer allows you to accurately measure the engine RPM and ensure it’s within the specified range. This is especially helpful for fine-tuning the high-speed jet. I recommend an inductive tachometer that clips onto the spark plug wire.
Spark Plug Wrench: To remove and inspect the spark plug.
Spark Plug Cleaner or Wire Brush: To clean the spark plug.
Fresh Fuel: Use the correct fuel mixture ratio as specified by Stihl (typically 50:1).
Clean Rags: For wiping up spills and cleaning components.
Work Gloves: To protect your hands.
Eye Protection: Safety glasses or goggles.
Ear Protection: Earplugs or earmuffs.
Stihl MS 250 Owner’s Manual: Refer to your owner’s manual for specific instructions and specifications for your chainsaw model.

Safety First!

Before you even think about touching your chainsaw, prioritize safety.

Read the Manual: Familiarize yourself with the Stihl MS 250 owner’s manual.
Wear Protective Gear: Always wear safety glasses, ear protection, gloves, and sturdy boots.
Work in a Well-Ventilated Area: Carburetor adjustment involves working with fuel, which can produce harmful fumes.
Ensure the Chainsaw is Cool: Never attempt to adjust the carburetor on a hot engine.
Disconnect the Spark Plug Wire: This prevents accidental starting.
Stable Work Surface: Place the chainsaw on a stable surface.
Fire Extinguisher: Keep a fire extinguisher nearby, just in case.

Step-by-Step Carburetor Adjustment Guide

Now, let’s get down to the nitty-gritty. This is where my years of experience come in handy. I’ve seen it all – from carburetors gummed up with old fuel to screws stripped from over-tightening. Follow these steps carefully, and you’ll have your Stihl MS 250 running like a champ in no time.

1. Initial Inspection and Preparation

Check the Spark Plug: Remove the spark plug and inspect it. A healthy spark plug should be clean and dry with a light tan color. If it’s black and sooty, it indicates a rich mixture. If it’s white and ashy, it indicates a lean mixture. Clean or replace the spark plug as needed. I’ve found that replacing the spark plug annually, especially with heavy use, can make a significant difference in performance.
Check the Air Filter: A dirty air filter restricts airflow and can cause the engine to run rich. Remove the air filter and clean it with compressed air or warm, soapy water. Allow it to dry completely before reinstalling. I once had a chainsaw that wouldn’t start, and after hours of troubleshooting, it turned out to be a completely clogged air filter!
Check the Fuel Filter: A clogged fuel filter restricts fuel flow and can cause the engine to run lean. Locate the fuel filter inside the fuel tank and inspect it. If it’s dirty or clogged, replace it. I typically replace my fuel filter every six months, especially when using ethanol-blended fuel.
Use Fresh Fuel: Old or stale fuel can cause carburetor problems. Drain the old fuel from the tank and replace it with fresh fuel mixed with the correct amount of two-stroke oil (50:1 for most Stihl models). I always use a fuel stabilizer to prevent fuel from going bad, especially during the off-season.

2. Locating the Carburetor Adjustment Screws

The carburetor adjustment screws are typically located on the side of the carburetor, near the engine. On the Stihl MS 250, you’ll usually find three screws:

H (High-Speed Jet): Controls fuel flow at high engine speeds.
L (Low-Speed Jet): Controls fuel flow at low engine speeds.
LA/T (Idle Speed Screw): Controls the idle speed of the engine.

Refer to your owner’s manual for the exact location of these screws on your specific model.

3. Understanding the Adjustment Process

The goal of carburetor adjustment is to achieve the optimal air/fuel mixture for smooth idling, responsive acceleration, and maximum power without causing engine damage.

Start with the Factory Settings: The factory settings are a good starting point. Refer to your owner’s manual for the recommended factory settings for the H and L screws. Typically, this involves turning the screws clockwise until they are lightly seated, then backing them out a specific number of turns (e.g., 1 turn).
Adjust the Low-Speed Jet (L): This is the most crucial adjustment for smooth idling and acceleration.
- Start the Engine: Start the chainsaw and let it warm up for a few minutes.
- Adjust the L Screw: Slowly turn the L screw clockwise (leaner) or counterclockwise (richer) until the engine idles smoothly and accelerates without hesitation.
- Listen to the Engine: A lean mixture will cause the engine to idle too fast and sound “raspy.” A rich mixture will cause the engine to idle roughly and produce excessive smoke.
- Fine-Tune: Make small adjustments to the L screw until you find the sweet spot where the engine idles smoothly and accelerates cleanly.
Adjust the Idle Speed Screw (LA/T): This screw adjusts the throttle plate opening and controls the idle speed.
- Check the Chain: Ensure the chain is not moving at idle. If it is, the idle speed is too high.
- Adjust the LA/T Screw: Turn the LA/T screw clockwise to increase the idle speed or counterclockwise to decrease the idle speed.
- Target Idle Speed: Aim for an idle speed that is high enough to prevent stalling but low enough to prevent the chain from moving. Stihl typically recommends an idle speed of around 2,800 RPM for the MS 250, but always consult your owner’s manual.
Adjust the High-Speed Jet (H): This adjustment is critical for maximizing power and preventing engine damage at high speeds.
- Use a Tachometer: A tachometer is highly recommended for accurately adjusting the H screw.
- Find a Safe Cutting Area: Choose a safe area where you can make a test cut into a log.
- Make a Test Cut: Engage the throttle fully and make a cut into the log.
- Monitor the RPM: Use the tachometer to monitor the engine RPM.
- Adjust the H Screw: Slowly turn the H screw clockwise (leaner) or counterclockwise (richer) until the engine reaches its maximum RPM without exceeding the specified limit. Stihl typically recommends a maximum RPM of around 12,500 RPM for the MS 250, but always consult your owner’s manual.
- Listen to the Engine: A lean mixture at high speed will cause the engine to sound “screaming” or “whining.” A rich mixture will cause the engine to sound “bogged down” or “muffled.”
- Fine-Tune: Make small adjustments to the H screw until you find the sweet spot where the engine reaches its maximum RPM without sounding lean or rich.
Test and Refine: After making these adjustments, test the chainsaw by cutting several pieces of wood. Pay attention to how the engine performs and make further adjustments as needed.

4. Dealing with Common Carburetor Issues

Chainsaw Won’t Start:
- Check the Fuel: Make sure there is fresh fuel in the tank.
- Check the Spark Plug: Ensure the spark plug is clean and firing properly.
- Check the Air Filter: Make sure the air filter is clean.
- Check the Fuel Filter: Make sure the fuel filter is clean.
- Prime the Carburetor: Press the primer bulb several times to prime the carburetor.
- Adjust the L Screw: Try adjusting the L screw slightly richer (counterclockwise).
Chainsaw Idles Poorly:
- Adjust the L Screw: Fine-tune the L screw until the engine idles smoothly.
- Adjust the LA/T Screw: Adjust the LA/T screw to achieve the correct idle speed.
- Check for Air Leaks: Inspect the carburetor and intake manifold for air leaks.
Chainsaw Lacks Power:
- Adjust the H Screw: Fine-tune the H screw to maximize power at high speeds.
- Check the Spark Arrestor Screen: A clogged spark arrestor screen can restrict exhaust flow and reduce power.
- Check the Chain: Make sure the chain is sharp and properly tensioned.
Chainsaw Smokes Excessively:
- Adjust the L and H Screws: A rich mixture can cause excessive smoke. Lean out the mixture by turning the L and H screws clockwise.
- Check the Fuel Mixture: Make sure you are using the correct fuel mixture ratio (50:1 for most Stihl models).

5. Practical Tips and Insights from My Experience

Use High-Quality Fuel: I always recommend using premium gasoline and a high-quality two-stroke oil. This will help to keep your carburetor clean and prevent fuel-related problems.
Clean Your Chainsaw Regularly: Regularly clean your chainsaw to remove sawdust and debris. This will help to prevent overheating and extend the life of your chainsaw.
Store Your Chainsaw Properly: When storing your chainsaw for an extended period, drain the fuel tank and run the engine until it stalls. This will prevent fuel from going bad and gumming up the carburetor.
Consider an Ultrasonic Carburetor Cleaner: For heavily clogged carburetors, an ultrasonic cleaner can be a lifesaver. These devices use sound waves to agitate and remove deposits from the carburetor’s internal passages. I’ve revived several seemingly hopeless carburetors using this method.
Document Your Settings: Once you’ve found the optimal settings for your carburetor, write them down! This will make it easier to return to those settings if you ever need to readjust the carburetor in the future.

6. Chainsaw Maintenance Beyond Carburetor Adjustment

Carburetor adjustment is only one piece of the puzzle. Regular maintenance is key to keeping your Stihl MS 250 running smoothly for years to come.

Chain Sharpening: A sharp chain is essential for efficient cutting and safety. Learn how to sharpen your chain using a file or a chain grinder. I prefer using a file for quick touch-ups in the field and a grinder for more thorough sharpening.
Chain Tension: Regularly check and adjust the chain tension. A loose chain can derail and cause injury. A tight chain can overheat and damage the bar and chain.
Bar Maintenance: Clean the bar groove regularly to remove sawdust and debris. Check the bar for wear and damage.
Lubrication: Use a high-quality bar and chain oil to lubricate the chain and bar. This will reduce friction and wear.
Cooling System: Keep the cooling fins on the cylinder clean to prevent overheating.
Exhaust System: Check the exhaust port and spark arrestor screen for carbon buildup. Clean them as needed.
Regular Inspection: Periodically inspect your chainsaw for loose screws, damaged parts, and other potential problems.

7. Case Study: Reviving a Neglected Stihl MS 250

I once acquired a used Stihl MS 250 that had been neglected for years. It wouldn’t start, and the carburetor was completely gummed up with old fuel. Here’s how I brought it back to life:

Thorough Cleaning: I disassembled the carburetor and cleaned each component with carburetor cleaner. I used a small wire brush to remove stubborn deposits.
Ultrasonic Cleaning: I soaked the carburetor body in an ultrasonic cleaner for 30 minutes.
New Parts: I replaced the fuel filter, fuel lines, and spark plug.
Carburetor Adjustment: I followed the steps outlined above to adjust the carburetor.
Chain Sharpening: I sharpened the chain and adjusted the chain tension.
Test Run: After all this work, the chainsaw started on the second pull and ran like new!

This experience taught me the importance of regular maintenance and the power of a thorough cleaning.

8. Wood Type Selection and Firewood Preparation

The Stihl MS 250 is a great saw for processing most firewood species. However, knowing your wood is essential.

Hardwoods vs. Softwoods: Hardwoods like oak, maple, and ash burn hotter and longer than softwoods like pine and fir. However, softwoods are easier to split and dry faster.
Green vs. Seasoned Wood: Green wood has a high moisture content and is difficult to burn. Seasoned wood has been dried for at least six months and burns much more efficiently.
Splitting Techniques: Use a splitting axe or a hydraulic log splitter to split firewood. Hydraulic splitters are much faster and easier, especially for large logs. I’ve found that a 20-ton hydraulic splitter is sufficient for most firewood needs.
Stacking Firewood: Stack firewood in a single row, allowing for good air circulation. This will help the wood to dry faster. I typically stack my firewood in a sunny, windy location.
Drying Time: The drying time for firewood depends on the species of wood, the climate, and the stacking method. It typically takes at least six months for firewood to dry properly. I use a moisture meter to check the moisture content of my firewood before burning it. The ideal moisture content is below 20%.

9. Costs, Materials, and Timing Estimates

Carburetor Adjustment: The cost of adjusting the carburetor yourself is minimal, as it only requires a screwdriver and some time.
Replacement Parts: Replacement parts, such as spark plugs, air filters, and fuel filters, are relatively inexpensive.
Tachometer: A good quality tachometer can cost between $30 and $100.
Hydraulic Log Splitter: A hydraulic log splitter can cost between $500 and $2,000, depending on the size and features.
Fuel: The cost of fuel will depend on the price of gasoline and the amount of firewood you process.
Two-Stroke Oil: High-quality two-stroke oil can cost between $10 and $20 per quart.
Drying Time: The drying time for firewood can range from six months to two years, depending on the species of wood and the climate.

10. Strategic Advantages of a Well-Tuned Chainsaw

A well-tuned chainsaw offers several strategic advantages for firewood preparation:

Increased Efficiency: A properly tuned chainsaw will cut faster and more efficiently, saving you time and energy.
Reduced Fuel Consumption: A well-tuned chainsaw will burn less fuel, saving you money.
Extended Engine Life: A properly tuned chainsaw will run cooler and cleaner, extending the life of the engine.
Improved Safety: A well-tuned chainsaw is less likely to stall or malfunction, reducing the risk of accidents.
Greater Enjoyment: A well-tuned chainsaw is simply more enjoyable to use.

Practical Next Steps

Gather Your Tools and Materials: Assemble all the tools and materials you’ll need for carburetor adjustment.
Inspect Your Chainsaw: Thoroughly inspect your chainsaw for any problems, such as a dirty air filter or a fouled spark plug.
Locate the Adjustment Screws: Refer to your owner’s manual to locate the carburetor adjustment screws.
Start the Engine: Start the chainsaw and let it warm up for a few minutes.
Adjust the Carburetor: Follow the steps outlined above to adjust the carburetor.
Test and Refine: Test the chainsaw by cutting several pieces of wood and make further adjustments as needed.
Maintain Your Chainsaw: Regularly maintain your chainsaw to keep it running smoothly for years to come.

Conclusion

Adjusting the carburetor on your Stihl MS 250 might seem daunting at first, but with a little knowledge and patience, it’s a skill anyone can master. Remember, a well-tuned chainsaw is not just a tool; it’s an investment in efficiency, safety, and the satisfaction of a job well done. So, grab your screwdriver, put on your safety glasses, and get ready to unleash the full potential of your Stihl MS 250. Happy cutting! And remember, always prioritize safety and consult your owner’s manual for specific instructions related to your model.

Stihl MS 250 Carburetor Adjustment (Easy Tune-Up Tips for Firewood)