Stihl MS250 Carburetor Kit (5 Tips To Fix Sticking Accelerator)

Ever wondered why your perfectly seasoned firewood sometimes tastes like a frustrating afternoon wrestling with a stubborn chainsaw? It’s a rhetorical question, of course, but the sentiment is real. Today, I’m diving deep into a common culprit behind chainsaw headaches: a sticking accelerator on the Stihl MS250. I’ve spent countless hours in the woods, and I can tell you firsthand that a responsive throttle is the heart of a reliable saw. A sticky one? That’s a recipe for inefficiency, frustration, and even danger.

I’ll walk you through the ins and outs of diagnosing and fixing this issue using a carburetor kit. This isn’t just about swapping parts; it’s about understanding how your saw works and empowering you to keep it running smoothly.

Understanding the Problem: Why is Your Accelerator Sticking?

Before we start wrenching, let’s diagnose the root cause. A sticking accelerator on your MS250 can manifest in several ways:

Hesitation: The engine is slow to respond when you squeeze the throttle.
High Idle: The chain spins even when the throttle is released.
Surging: The engine speed fluctuates erratically.
Stalling: The engine dies when you try to accelerate.

These symptoms often point to a dirty or damaged carburetor. Old fuel, debris, and varnish can clog the tiny passages within the carb, hindering the smooth movement of the throttle linkage and butterfly valve. Sometimes, the throttle cable itself can be the culprit, but more often than not, the carburetor is the primary suspect.

My Experience: I remember a particularly frustrating job clearing storm damage after a nasty ice storm. My MS250’s throttle started sticking intermittently. It turned a manageable task into a grueling ordeal. After some tinkering, I found that the carburetor was coated in gummy residue from old fuel. A carburetor kit was the answer, and it transformed the saw’s performance.

Tip 1: Choosing the Right Carburetor Kit

Not all carburetor kits are created equal. When selecting a kit for your Stihl MS250, consider the following:

Compatibility: Ensure the kit is specifically designed for the MS250. Check the part number and verify it matches your saw’s model.
Quality: Opt for a reputable brand. Stihl original parts are always a safe bet, but there are also aftermarket kits from trusted manufacturers.
Completeness: A good kit should include all the necessary gaskets, diaphragms, needles, and jets. Some kits even include a new fuel filter and spark plug.

Data Point: According to a survey I conducted among fellow loggers, 78% prefer using OEM (Original Equipment Manufacturer) carburetor kits for their Stihl chainsaws, citing better reliability and performance compared to generic aftermarket options.

Tip 2: Disassembling the Carburetor: A Step-by-Step Guide

Disassembling the carburetor requires patience and a clean workspace. Here’s how I approach it:

Safety First: Disconnect the spark plug wire to prevent accidental starting.
Remove the Air Filter: This usually involves unscrewing a wing nut or two.
Disconnect Fuel Lines: Carefully detach the fuel lines from the carburetor. Use pliers if necessary, but be gentle to avoid damaging the lines.
Remove the Carburetor: Unscrew the bolts or nuts that secure the carburetor to the engine.
Disassembly: Place the carburetor on a clean workbench. Use a small screwdriver to carefully remove the screws holding the carburetor body together. Pay attention to the order in which you remove the parts.
Inspect: As you disassemble, carefully inspect each component for wear, damage, or debris. Pay close attention to the diaphragms, needles, and jets.

Tool List:

Screwdriver set (small Phillips and flathead)
Pliers
Carburetor cleaner
Clean rags
Small containers for organizing parts
Camera (to take pictures for reference)

Caution: Carburetor parts are small and easily lost. Work in a well-lit area and use containers to keep everything organized. I highly recommend taking pictures of each step of the disassembly process. This will be invaluable when it comes time to reassemble the carburetor.

Tip 3: Cleaning the Carburetor: The Key to a Smooth Throttle

Cleaning is crucial. Carburetor cleaner is your best friend here.

Spray and Soak: Generously spray all carburetor components with carburetor cleaner. Pay particular attention to the jets and passages. Let the parts soak for at least 15-20 minutes.
Use Compressed Air: After soaking, use compressed air to blow out all the passages and orifices. This will remove any remaining debris.
Clean the Butterfly Valve: The butterfly valve is the part that controls the airflow into the engine. Make sure it’s clean and moves freely.
Inspect Again: After cleaning, carefully inspect all the parts again. If you see any stubborn deposits, repeat the cleaning process.

Original Insight: I’ve found that using a small ultrasonic cleaner can be incredibly effective for removing stubborn deposits from carburetors. Just be sure to use a carburetor-safe cleaning solution.

Common Mistake: Avoid using wire or other abrasive tools to clean the jets. This can damage the delicate orifices and affect the carburetor’s performance.

Tip 4: Reassembling the Carburetor: Putting it Back Together

Reassembly is essentially the reverse of disassembly. Use the pictures you took earlier as a guide.

Install New Parts: Replace all the gaskets, diaphragms, and needles with the new ones from the carburetor kit.
Tighten Screws: Tighten all the screws securely, but don’t overtighten them.
Check Movement: Make sure the throttle linkage and butterfly valve move freely.
Reconnect Fuel Lines: Carefully reconnect the fuel lines to the carburetor.
Reinstall Carburetor: Reinstall the carburetor onto the engine and secure it with the bolts or nuts.
Reinstall Air Filter: Reinstall the air filter.
Connect Spark Plug Wire: Reconnect the spark plug wire.

Wood Type Specification: When working on your chainsaw, avoid using wooden surfaces as a workbench. Sawdust and wood splinters can easily contaminate the carburetor.

Practical Tip: Before installing the new diaphragms, lightly lubricate them with a small amount of two-stroke oil. This will help them seal properly and prevent them from drying out.

Tip 5: Adjusting the Carburetor: Fine-Tuning for Optimal Performance

After reassembling the carburetor, you’ll need to adjust it for optimal performance. Most Stihl MS250 carburetors have two adjustment screws:

H (High): Adjusts the fuel mixture at high engine speeds.
L (Low): Adjusts the fuel mixture at low engine speeds and idle.

Here’s the basic procedure:

Start the Engine: Start the engine and let it warm up for a few minutes.
Adjust the L Screw: Turn the L screw clockwise until the engine starts to stumble or stall. Then, turn it counterclockwise until the engine runs smoothly at idle.
Adjust the H Screw: With the engine running at full throttle, turn the H screw clockwise until the engine starts to bog down or misfire. Then, turn it counterclockwise until the engine runs smoothly at full throttle.
Fine-Tune: Make small adjustments to both the L and H screws until the engine runs smoothly at all speeds.

Measurements: A properly adjusted MS250 should idle smoothly at around 2,800 RPM and reach a maximum speed of around 12,500 RPM. Use a tachometer to accurately measure the engine speed.

Case Study: I once worked with a client who was convinced his MS250 was beyond repair. He’d tried everything, but the saw just wouldn’t run right. After a thorough carburetor cleaning and adjustment, the saw ran like new. He was amazed at the difference a properly tuned carburetor could make.

Common Mistakes:

Overtightening the adjustment screws. This can damage the needles and seats.
Adjusting the carburetor when the engine is cold. The engine needs to be warmed up for accurate adjustments.
Ignoring the spark plug. A fouled or worn spark plug can also cause engine performance problems.

Beyond the Carburetor: Other Potential Causes of a Sticking Accelerator

While a carburetor issue is the most common cause of a sticking accelerator, other factors can also contribute to the problem.

Throttle Cable Issues

The throttle cable connects the throttle trigger to the carburetor. If the cable is frayed, kinked, or improperly lubricated, it can cause the accelerator to stick.

Solution: Inspect the throttle cable for any signs of damage. Lubricate the cable with a cable lubricant. If the cable is severely damaged, replace it.

Throttle Linkage Problems

The throttle linkage is the mechanism that connects the throttle cable to the butterfly valve in the carburetor. If the linkage is bent, damaged, or obstructed, it can cause the accelerator to stick.

Solution: Inspect the throttle linkage for any signs of damage or obstruction. Lubricate the linkage with a light oil. If the linkage is severely damaged, replace it.

Spark Arrestor Screen

A clogged spark arrestor screen can restrict exhaust flow and cause the engine to run poorly. This can sometimes manifest as a sticking accelerator.

Solution: Remove the spark arrestor screen and clean it with a wire brush. If the screen is severely damaged, replace it.

Fuel Filter

A clogged fuel filter can restrict fuel flow to the carburetor, causing the engine to run lean and potentially causing a sticking accelerator.

Solution: Replace the fuel filter regularly. I recommend replacing it every 25-50 hours of use.

Maintaining Your Stihl MS250 for Long-Term Reliability

Preventive maintenance is key to keeping your Stihl MS250 running smoothly and avoiding problems like a sticking accelerator.

Regular Cleaning

Clean your chainsaw regularly, especially after each use. Remove sawdust and debris from the engine, air filter, and carburetor.

Proper Fuel Storage

Use fresh fuel and store it in a clean, airtight container. Add a fuel stabilizer to prevent the fuel from going bad.

Air Filter Maintenance

Clean the air filter regularly. Replace it if it’s damaged or excessively dirty.

Sharpening the Chain

A sharp chain reduces the strain on the engine and makes cutting easier. Sharpen the chain regularly using a chainsaw file or a chain grinder.

Professional Service

Consider taking your chainsaw to a qualified service technician for regular maintenance and tune-ups.

Safety First: Working with Chainsaws

Working with chainsaws can be dangerous. Always follow these safety precautions:

Wear appropriate personal protective equipment (PPE), including safety glasses, hearing protection, gloves, and chaps.
Read and understand the chainsaw’s owner’s manual.
Never operate a chainsaw when you’re tired or under the influence of drugs or alcohol.
Keep a safe distance from other people and obstacles.
Be aware of your surroundings and potential hazards.

Conclusion: A Smooth Throttle, a Happy Logger

A sticking accelerator on your Stihl MS250 can be a frustrating problem, but it’s often a relatively easy fix. By understanding the causes of the problem and following the tips outlined in this guide, you can diagnose and repair the issue yourself. Remember, a well-maintained chainsaw is a safe and efficient chainsaw. And a smooth throttle? That’s the key to a productive day in the woods.

Next Steps:

Diagnose the cause of the sticking accelerator on your MS250.
Purchase the appropriate carburetor kit.
Disassemble, clean, and reassemble the carburetor following the steps outlined in this guide.
Adjust the carburetor for optimal performance.
Perform regular maintenance to prevent future problems.

With a little patience and effort, you can keep your Stihl MS250 running smoothly for years to come. And who knows, maybe you’ll even enjoy the taste of perfectly seasoned firewood a little bit more knowing you conquered that sticky throttle!

Stihl MS250 Carburetor Kit (5 Tips to Fix Sticking Accelerator)