Stihl MS 250 Carburetor Adjustment (3 Pro Tips For Peak Power)

Let’s dive into the heart of your Stihl MS 250 and unlock its true potential! I’m going to show you how to adjust the carburetor for peak performance. Don’t worry, it’s not as daunting as it sounds. I’ll break it down into easy-to-follow steps, sharing pro tips I’ve learned over years of working with chainsaws. We’ll get your saw purring like a kitten and ripping through wood like a beast in no time.

Stihl MS 250 Carburetor Adjustment: 3 Pro Tips for Peak Power

The Stihl MS 250 is a workhorse. It’s a popular choice for homeowners and professionals alike because it’s relatively lightweight, powerful enough for a wide range of tasks, and generally reliable. However, like any machine, it needs proper maintenance, and that includes carburetor adjustment. A properly tuned carb ensures optimal fuel-air mixture, leading to better performance, fuel efficiency, and a longer engine life.

According to recent data from the U.S. Energy Information Administration, residential wood heating accounts for a significant portion of home heating energy consumption, especially in rural areas. Having a well-maintained chainsaw like the MS 250 is crucial for efficient firewood preparation.

Before we get started, let’s be clear: messing with your carburetor can be tricky. If you’re not comfortable, take your saw to a qualified technician. But if you’re up for the challenge, read on! I’ll walk you through it.

Why Carburetor Adjustment Matters

Think of your chainsaw’s carburetor as the chef in a fine-dining restaurant. It’s responsible for mixing the perfect blend of air and fuel for combustion. Too much fuel (a “rich” mixture), and your saw will run sluggishly, produce excessive smoke, and potentially foul the spark plug. Too little fuel (a “lean” mixture), and your saw will overheat, lose power, and could even suffer engine damage.

I remember one time, back in my early days of logging, I ignored a lean-running saw. I kept pushing it, thinking it was just a “tough” piece of wood. Big mistake! I ended up with a scored piston and a hefty repair bill. Lesson learned: pay attention to your saw’s performance, and don’t ignore the signs of a poorly adjusted carburetor.

Here are some telltale signs that your MS 250 carburetor needs adjustment:

Difficult starting: The saw takes multiple pulls to start, especially when cold.
Rough idling: The engine idles unevenly or stalls frequently.
Poor acceleration: The saw hesitates or bogs down when you try to accelerate.
Excessive smoke: The exhaust is black and smoky, indicating a rich mixture.
Overheating: The engine gets excessively hot, indicating a lean mixture.
Loss of power: The saw lacks the power it used to have, especially when cutting larger logs.

Safety First!

Before you even think about touching your chainsaw, make sure you’re wearing appropriate safety gear:

Eye protection: Safety glasses or a face shield are essential to protect your eyes from flying debris.
Hearing protection: Chainsaws are loud! Wear earplugs or earmuffs to prevent hearing damage.
Gloves: Protect your hands from cuts and abrasions.
Long pants and sturdy boots: Protect your legs and feet from potential injuries.

Also, ensure the chainsaw is turned off and the chain brake is engaged. Disconnect the spark plug wire to prevent accidental starting. Work in a well-ventilated area, as you’ll be dealing with gasoline fumes.

Step-by-Step Carburetor Adjustment for the Stihl MS 250

The Stihl MS 250 carburetor typically has three adjustment screws:

L (Low-speed screw): Controls the fuel mixture at idle and low speeds.
H (High-speed screw): Controls the fuel mixture at high speeds and under load.
LA (Idle speed screw): Adjusts the engine idle speed.

Important Note: Some MS 250 models have limiter caps on the H and L screws. These caps are designed to restrict the adjustment range and prevent over-leaning the mixture. If your saw has these caps, you may need to remove them to achieve optimal performance. I’ll explain how to do that later.

Tools You’ll Need:

Screwdriver: A small, flat-blade screwdriver is typically used to adjust the carburetor screws. A “D” shaped screwdriver may be required if the limiter caps are present.
Tachometer (optional but recommended): A tachometer allows you to accurately measure the engine RPM and ensure it’s within the manufacturer’s specifications.
Spark plug wrench: For removing and inspecting the spark plug.
Cleaning supplies: A clean rag and carburetor cleaner to remove any dirt or debris.

Step 1: Locate the Carburetor Adjustment Screws

The carburetor is usually located behind the air filter housing. Remove the air filter cover and the air filter to expose the carburetor. You should see the three adjustment screws (L, H, and LA) clearly labeled.

Step 2: Initial Settings

Before making any adjustments, it’s a good idea to return the screws to their factory settings. This provides a baseline for your adjustments. The factory settings for the MS 250 are typically:

L screw: 1 turn out from fully closed.
H screw: 1 turn out from fully closed.

To find the closed position, gently turn the screw clockwise until it stops. Do not overtighten, as this can damage the carburetor. Then, turn the screw counterclockwise the specified number of turns.

Note: These are general guidelines. Refer to your owner’s manual for the specific factory settings for your MS 250 model.

Step 3: Adjusting the Idle Speed (LA Screw)

Start the chainsaw and let it warm up for a few minutes. Then, adjust the LA screw until the engine idles smoothly without the chain moving. If the chain is moving at idle, turn the LA screw counterclockwise to reduce the idle speed. If the engine stalls at idle, turn the LA screw clockwise to increase the idle speed.

The ideal idle speed for the MS 250 is around 2,800 RPM. If you have a tachometer, use it to accurately measure the idle speed.

Step 4: Adjusting the Low-Speed (L) Screw

The L screw affects the engine’s performance at idle and low speeds. To adjust the L screw, slowly turn it clockwise until the engine starts to stumble or stall. Then, slowly turn it counterclockwise until the engine runs smoothly and accelerates cleanly.

Here’s a trick I use: Listen carefully to the engine as you adjust the L screw. You’re looking for the “sweet spot” where the engine responds quickly and smoothly to throttle changes. If the engine hesitates or bogs down when you accelerate, turn the L screw slightly counterclockwise. If the engine runs roughly or smokes excessively at idle, turn the L screw slightly clockwise.

Step 5: Adjusting the High-Speed (H) Screw

The H screw controls the fuel mixture at high speeds and under load. This is the most critical adjustment, as a lean mixture can cause engine damage.

Important: If your MS 250 has limiter caps on the H screw, you may need to remove them to achieve optimal performance. I’ll explain how to do that in the next section.

To adjust the H screw, run the chainsaw at full throttle and listen to the engine. You’re looking for a smooth, consistent sound. If the engine sounds “raspy” or “screaming,” it’s running lean. Turn the H screw slightly counterclockwise to richen the mixture. If the engine sounds “muffled” or “bogged down,” it’s running rich. Turn the H screw slightly clockwise to lean the mixture.

Use a tachometer to ensure the engine RPM is within the manufacturer’s specifications. The maximum RPM for the MS 250 is typically around 12,500-13,000 RPM. Exceeding this limit can damage the engine.

Here’s my pro tip: When adjusting the H screw, make small adjustments (no more than 1/8 of a turn at a time) and give the engine a few seconds to respond. It’s better to err on the side of caution and run slightly rich than to run lean.

Step 6: Fine-Tuning and Testing

Once you’ve adjusted the L and H screws, let the engine cool down completely. Then, start it up again and repeat the adjustment process. This allows you to fine-tune the carburetor for optimal performance.

Test the chainsaw under load by cutting a few logs. Pay attention to the engine’s performance and adjust the carburetor as needed. If the saw bogs down when cutting, richen the mixture slightly by turning the H screw counterclockwise. If the saw smokes excessively, lean the mixture slightly by turning the H screw clockwise.

Removing Limiter Caps (If Applicable)

As I mentioned earlier, some MS 250 models have limiter caps on the H and L screws. These caps restrict the adjustment range and can prevent you from achieving optimal performance.

To remove the limiter caps, you’ll need a small screwdriver or a pick. Carefully pry the caps off the screws. Be careful not to damage the screws or the carburetor body.

Once the caps are removed, you’ll have full access to the adjustment screws. Follow the steps above to adjust the carburetor for peak performance.

Important: Removing the limiter caps may void your warranty. Also, it’s important to understand the risks of running a lean mixture. If you’re not comfortable making these adjustments, take your saw to a qualified technician.

Pro Tips for Peak Power and Longevity

Now that you know how to adjust the carburetor, here are a few more pro tips to help you get the most out of your Stihl MS 250:

Use High-Quality Fuel and Oil: Always use fresh, high-octane gasoline and a high-quality two-stroke oil mixed at the proper ratio (typically 50:1). This will ensure optimal engine performance and longevity. I personally prefer using Stihl’s own Ultra HP two-stroke oil. It’s a bit more expensive, but it provides excellent lubrication and helps keep the engine clean.
Clean the Air Filter Regularly: A dirty air filter restricts airflow and can cause the engine to run poorly. Clean the air filter regularly with soap and water. Let it dry completely before reinstalling it. In dusty conditions, you may need to clean the air filter more frequently.
Sharpen the Chain Regularly: A dull chain puts unnecessary strain on the engine and reduces cutting efficiency. Sharpen the chain regularly with a file or a chain grinder. I prefer using a file, as it gives me more control over the sharpening process. There’s something deeply satisfying about hand sharpening a chain, a skill passed down through generations.
Inspect the Spark Plug Regularly: The spark plug is a window into the engine’s health. Inspect the spark plug regularly for signs of fouling or damage. A healthy spark plug should be clean and dry with a light tan color. If the spark plug is black and oily, it indicates a rich mixture. If the spark plug is white and dry, it indicates a lean mixture. Replace the spark plug as needed.
Maintain Proper Chain Tension: Proper chain tension is essential for safe and efficient cutting. The chain should be snug against the bar but still able to be pulled around by hand. Too much tension can cause the chain to bind and overheat. Too little tension can cause the chain to derail.
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 the fuel from gumming up the carburetor. Also, remove the chain and bar and clean them thoroughly. Store the chainsaw in a dry, well-ventilated area.
Understand Your Wood: Knowing the wood you are processing is essential. Different species have varying densities and moisture content, impacting cutting performance and fuel efficiency. For example, oak is a dense hardwood that requires more power than pine, a softwood. Seasoning wood properly is crucial for firewood. Green wood contains high moisture levels, making it difficult to burn efficiently and producing excessive smoke. Aim for a moisture content of 20% or less for optimal burning. I use a moisture meter to check the moisture content of my firewood before stacking it for the winter.
Safety is Paramount: Always prioritize safety when operating a chainsaw. Wear appropriate safety gear, be aware of your surroundings, and never operate a chainsaw when you’re tired or distracted. Chainsaws are powerful tools, but they can be dangerous if not used properly.

Case Study: Reviving a Sluggish Stihl MS 250

I had a friend, let’s call him Tom, who was about to give up on his MS 250. He said it was running rough, wouldn’t idle properly, and lacked power. He was convinced it was time for a new saw.

I offered to take a look. After a quick inspection, I determined that the carburetor was the culprit. The L and H screws were way out of adjustment, and the air filter was clogged with sawdust.

I cleaned the air filter, returned the carburetor screws to their factory settings, and then followed the adjustment procedure I’ve outlined above. After a few minutes of tweaking, the saw was running like new! Tom was amazed. He couldn’t believe the difference a simple carburetor adjustment could make.

This case study highlights the importance of regular maintenance and proper carburetor adjustment. It can save you money, extend the life of your chainsaw, and improve its performance.

Cost Considerations

The cost of maintaining a Stihl MS 250 can vary depending on the amount of use and the type of maintenance required. Here’s a breakdown of some common costs:

Fuel: The cost of fuel will depend on the price of gasoline and the amount of use.
Two-stroke oil: A good quality two-stroke oil can cost around $10-$20 per quart.
Air filter: Air filters typically cost around $5-$10.
Spark plug: Spark plugs typically cost around $5-$10.
Chain: Chains can cost anywhere from $20-$50, depending on the length and type.
Bar: Bars can cost anywhere from $30-$100, depending on the length and type.
Carburetor rebuild kit: Carburetor rebuild kits typically cost around $20-$40.
Professional service: If you’re not comfortable performing maintenance yourself, you can take your chainsaw to a qualified technician. Labor rates typically range from $50-$100 per hour.

By performing regular maintenance yourself, you can save money and extend the life of your chainsaw.

Troubleshooting Common Issues

Here are some common issues you might encounter when adjusting your Stihl MS 250 carburetor and how to troubleshoot them:

Engine won’t start: Check the fuel level, spark plug, and air filter. Make sure the choke is engaged. If the engine still won’t start, the carburetor may be clogged or need rebuilding.
Engine idles rough: Adjust the LA screw to increase or decrease the idle speed. If the engine still idles rough, the L screw may need adjustment.
Engine bogs down when accelerating: Adjust the L screw counterclockwise to richen the mixture.
Engine lacks power: Adjust the H screw counterclockwise to richen the mixture. Make sure the chain is sharp and properly tensioned.
Engine overheats: Adjust the H screw counterclockwise to richen the mixture. Check the cooling fins for debris.
Engine smokes excessively: Adjust the H screw clockwise to lean the mixture.
Chain moves at idle: Adjust the LA screw counterclockwise to reduce the idle speed.

Next Steps and Additional Resources

Now that you’ve learned how to adjust your Stihl MS 250 carburetor, you’re well on your way to achieving peak power and performance. Remember to always prioritize safety and follow the manufacturer’s instructions.

Here are some additional resources that you may find helpful:

Stihl Owner’s Manual: Your owner’s manual contains valuable information about your chainsaw, including maintenance procedures and troubleshooting tips.
Stihl Website: The Stihl website (www.stihl.com) offers a wealth of information about their products, including FAQs, troubleshooting guides, and parts diagrams.
Chainsaw Forums: Online chainsaw forums are a great place to connect with other chainsaw enthusiasts and get advice from experienced users.
Local Stihl Dealer: Your local Stihl dealer can provide expert advice and service for your chainsaw.

Suppliers of Logging Tools and Equipment:

Baileys: Baileys is a well-known supplier of logging tools and equipment, offering a wide range of products at competitive prices.
Northern Tool + Equipment: Northern Tool + Equipment carries a variety of logging tools and equipment, as well as other tools and supplies.
Forestry Suppliers, Inc.: Forestry Suppliers, Inc. specializes in providing equipment and supplies for forestry, surveying, and other related industries.

Drying Equipment Rental Services:

Sunbelt Rentals: Sunbelt Rentals offers a variety of drying equipment for rent, including dehumidifiers and air movers.
United Rentals: United Rentals also offers a wide range of drying equipment for rent, as well as other construction equipment.

By following these tips and resources, you can keep your Stihl MS 250 running smoothly for years to come. Happy cutting! Remember, a little elbow grease and attention to detail can go a long way in keeping your chainsaw in top shape. After all, as they say in the logging world, “A sharp chain and a well-tuned saw are a logger’s best friends.” Now, go forth and conquer that woodpile!

Stihl MS 250 Carburetor Adjustment (3 Pro Tips for Peak Power)