How To Start A Stihl MS 251 Chainsaw: Tips, Troubleshooting, And Common Issues [Updated On- 2026]

To start a STIHL MS 251 chainsaw, follow these steps: 1) Prime the fuel system 3-5 times. 2) Squeeze the throttle trigger and set the control lever to the full choke position. 3) Lock the lever. 4) Pull the starter cord straight up until the engine runs. For warm starts, repeat without using full choke.

If the engine does not start, check for common issues. Ensure there is fuel in the tank and that the fuel mixture is correct. Inspect the spark plug for damage or dirt. If the chainsaw struggles to start, the primer bulb may require additional pressing to establish fuel flow.

The Stihl MS 251 chainsaw can experience other problems during operation. Common issues include a dull chain, improper tension, or clogged air filters. Regular maintenance is essential for optimal performance. Next, we will explore maintenance techniques to keep your Stihl MS 251 chainsaw in peak condition, ensuring reliability and efficiency in every cutting task.

Table of Contents

What Preparations Are Necessary Before Starting a Stihl MS 251 Chainsaw?

To start a Stihl MS 251 Chainsaw, proper preparations are essential for safety and efficiency. Key preparations include checking fuel and oil levels, inspecting the chain tension, ensuring the safety features are functioning, and wearing appropriate personal protective equipment.

Check fuel and oil levels
Inspect chain tension
Ensure safety features function
Wear personal protective equipment

These preparations play a critical role in ensuring the smooth operation of the chainsaw and enhancing user safety.

Check Fuel and Oil Levels: Checking fuel and oil levels ensures the chainsaw operates efficiently. The Stihl MS 251 uses a mixture of gasoline and two-stroke engine oil. It is important to mix the fuel according to the manufacturer’s guidelines to prevent engine damage. Inadequate fuel may hinder performance, while insufficient oil can lead to chain damage. Users should regularly inspect the fuel level before use, and check that the oil reservoir is filled to the appropriate level.
Inspect Chain Tension: Inspecting chain tension is crucial for safe operation. The chain should be tight enough to stay on the bar but loose enough to allow smooth movement. If the chain is too loose, it may come off the bar during operation, creating a safety hazard. Users should adjust the tension using the tool provided, and check for any signs of wear on the chain and bar before starting.
Ensure Safety Features Function: Ensuring all safety features function properly enhances user safety. The Stihl MS 251 comes equipped with several safety features, including a chain brake, throttle lock, and protective hand guards. Users should check that the chain brake engages properly and that the throttle lock is operational. Ensuring these features work minimizes the risk of accidents during operation.
Wear Personal Protective Equipment: Wearing personal protective equipment (PPE) is vital for safety while using a chainsaw. Recommended PPE includes a helmet, eye protection, ear protection, gloves, and cut-resistant chaps. These items protect users from flying debris, noise, and potential cuts or injuries. By wearing appropriate PPE, users can significantly reduce the risk of injury while operating the chainsaw.

By thoroughly preparing before starting a Stihl MS 251, users can promote a safer and more effective cutting experience.

Which Fuel Type Is Recommended for a Stihl MS 251 Chainsaw?

The recommended fuel type for a Stihl MS 251 chainsaw is a mixture of unleaded gasoline and 2-stroke oil.

Use unleaded gasoline with a minimum octane rating of 89.
Use a 2-stroke oil that is specifically formulated for air-cooled engines.
Follow the correct fuel-oil ratio of 50:1 for the fuel mixture.
Avoid using fuel with ethanol content higher than 10%.
Store fuel in a clean, approved container.

To ensure optimal performance, it is crucial to understand the specifications behind these recommendations.

Unleaded Gasoline: Using unleaded gasoline with an octane rating of at least 89 prevents engine knocking. Engine knocking can lead to reduced performance and damage over time. Stihl emphasizes the importance of using high-quality fuel to avoid engine issues.
2-Stroke Oil: A 2-stroke oil formulated for air-cooled engines provides necessary lubrication to the engine. This oil is designed to burn cleanly, which minimizes carbon buildup. For instance, Stihl’s own oil, such as the HP Ultra, is highly recommended due to its quality and efficiency.
Fuel-Oil Ratio: The correct fuel-oil ratio of 50:1 means mixing 2.6 ounces of oil with one gallon of gasoline. This specific ratio ensures optimal lubrication and engine performance. Deviating from this ratio can lead to either smoking and carbon deposits or engine wear and failure.
Ethanol Content: Avoiding fuel with ethanol content greater than 10% is crucial. Ethanol can absorb moisture, which leads to problems like fuel separation and corrosion within the engine. According to a study by the Small Engine Manufacturers Association, ethanol can cause significant long-term damage, reducing the lifespan of small engines.
Storage Guidelines: Storing fuel in a clean, approved container protects it from contaminants and moisture. Contaminants can affect the fuel’s combustion properties, leading to engine performance issues. The EPA recommends using containers that comply with their regulations to ensure safety and efficiency in fuel storage.

These guidelines ensure reliability and prolong the lifespan of your Stihl MS 251 chainsaw. Adhering to these recommendations will help prevent common engine problems and improve overall performance.

How Can You Ensure the Oil Level Is Adequate in a Stihl MS 251 Chainsaw?

To ensure the oil level is adequate in a Stihl MS 251 chainsaw, check the oil reservoir, inspect the oil flow, and monitor oil usage.

Check the oil reservoir:
– Locate the oil reservoir on the chainsaw. It is typically found near the guide bar.
– Open the cap and visually inspect the oil level. The oil should cover the minimum indicator mark for safe operation.
– If the oil is below this mark, refill it with the appropriate type of chain oil as specified in the user manual.
Inspect the oil flow:
– Start the chainsaw and allow it to idle. Observe the oil output by inspecting the guide bar and chain.
– Look for a thin film of oil on the chain when it is running. This indicates that the oiling system is functioning correctly.
– If there is no oil visible, check for clogs in the oil delivery system, including the oil filter and ports.
Monitor oil usage:
– Monitor the chainsaw’s oil consumption during use. A properly functioning system should not consume oil excessively.
– If you notice a rapid decrease in the oil level, it could indicate an issue such as a leak or an improperly adjusted oil pump.

By following these steps, you can maintain the oil level and ensure safe and efficient operation of your Stihl MS 251 chainsaw. Regular maintenance will help prevent wear on the chain and bar, enhancing the lifespan of your equipment.

What Are the Step-by-Step Instructions to Start a Stihl MS 251 Chainsaw?

To start a Stihl MS 251 chainsaw, follow these step-by-step instructions.

Check the oil and fuel levels.
Ensure the chain brake is engaged.
Place the chainsaw on a flat surface.
Press the primer bulb until you see fuel.
Set the choke to the “closed” position.
Pull the starter grip to start the engine.
Adjust the choke to “open” once the engine starts.

These instructions provide a clear process, but other perspectives may consider factors such as safety precautions and maintenance tips for optimal performance.

Checking Oil and Fuel Levels:
Checking the oil and fuel levels ensures the chainsaw runs efficiently and safely.
Engaging the Chain Brake:
Engaging the chain brake prevents accidental chain movement during the starting process.
Maintaining a Flat Surface:
Starting the chainsaw on a flat surface promotes stability and control.
Using the Primer Bulb:
The primer bulb helps to supply fuel to the engine, critical for starting.
Adjusting the Choke:
The choke controls the air-fuel mixture, crucial for starting a cold engine.
Pulling the Starter Grip:
Pulling the starter grip engages the engine and initiates the starting process.
Choke Adjustment after Start:
Adjusting the choke after starting ensures the engine operates smoothly.

Checking the oil and fuel levels is crucial for the proper functioning of the Stihl MS 251 chainsaw. The fuel should be a mixture of gasoline and oil, typically in a 50:1 ratio. Stihl recommends using their specific two-stroke engine oil for optimal performance. Keeping both fuel and oil levels adequate prevents engine damage.

Engaging the chain brake is a vital safety feature. The chain brake stops the chain from moving, reducing the risk of injury when starting the chainsaw. Always ensure the brake is engaged before performing maintenance or transport.

Placing the chainsaw on a flat surface is key for stability. An uneven surface increases the risk of accidents during startup. Ensure you have a firm grip and steady footing.

Using the primer bulb is essential for delivering fuel to the carburetor. Pressing it several times helps to fill the fuel line, making it easier to start the chainsaw. If the engine does not start after a few pulls, additional priming may be necessary.

Adjusting the choke is important for cold starts. The choke restricts airflow and enriches the fuel mixture, helping in colder conditions. After the engine starts and warms, the choke should be adjusted to the open position to prevent flooding.

Pulling the starter grip effectively engages the engine. Use a smooth, steady motion to avoid damage. Ideally, you should pull until you feel resistance, then pull a bit more for a clean start.

After starting the chainsaw, adjust the choke to ensure a proper running condition. The engine needs to maintain a balanced air-fuel mixture to operate efficiently. A fully open choke allows the engine to run without excessive fuel.

By following these steps and considering safety and maintenance perspectives, you can successfully start your Stihl MS 251 chainsaw.

How Do You Position the Chainsaw for Starting?

To position a chainsaw for starting, follow these key steps: ensure a stable surface, engage the chain brake, and hold the saw securely while setting it up for ignition.

Ensure a stable surface: Place the chainsaw on a flat, stable surface to prevent it from moving during starting. This reduces the risk of accidents.
Engage the chain brake: Pull the chain brake lever to the forward position. This step locks the chain and reduces the risk of kickback, which is when the saw suddenly jerks in the opposite direction when the chain hits an object.
Hold the saw securely: Grip the rear handle with one hand and place your foot on the front handle. This position stabilizes the chainsaw while you start it. It prevents the saw from jumping or moving unexpectedly.
Position the starter cord: Ensure the starter cord is easily accessible by pulling it away from the engine. This allows you to start the saw without obstruction.
Follow correct starting procedures: After setting up, follow the manufacturer’s instructions for the starting sequence, which often involves setting the choke to the correct position while pulling the starter cord until the engine fires.

By adhering to these practices, you can safely start a chainsaw while minimizing the risk of injuries. Always wear appropriate safety gear, such as gloves and goggles, to ensure your safety during operation.

What Is the Correct Procedure for Engaging the Choke?

Engaging the choke refers to the process of adjusting the air-fuel mixture in an internal combustion engine to facilitate starting the engine when it is cold. Proper choke engagement enriches the fuel mixture, allowing the engine to start more easily.

According to the Engine Manufacturers Association, the choke is a critical component designed to aid cold engine startups. It creates a richer fuel mixture by limiting the amount of air entering the combustion chamber.

Choke engagement generally occurs in two steps: setting the choke to the closed position and starting the engine. The choke remains closed until the engine starts and warms up. After the engine runs smoothly, the choke should be gradually opened to resume normal operation.

The Society of Automotive Engineers defines engaging the choke as “restricting airflow to increase fuel vaporization,” which is essential for effective cold starts. This process enhances combustion efficiency in cold temperatures.

Various factors contribute to the need for choke engagement, including low ambient temperatures and engine design. Cold engines require richer mixtures for adequate fuel combustion.

Data from the U.S. Department of Energy indicates that nearly 40% of all engine failures could be associated with starting issues, particularly during cold weather. This statistic underscores the importance of proper choke usage.

Engaging the choke improperly can lead to engine flooding or difficulty starting, potentially damaging the engine over time. Proper engagement enhances engine longevity and performance.

In terms of health and environmental impact, efficient engine startups reduce fuel consumption and emissions. This contributes to improved air quality and lower greenhouse gas output.

Examples include outdoor power equipment like lawnmowers, where choke engagement can significantly affect starting performance. Using proper techniques leads to enhanced reliability and less frequent repairs.

To mitigate choke-related issues, manufacturers recommend consistent maintenance, including checking choke operation and adjusting settings as necessary. Following these recommendations fosters efficient performance and longevity of machinery.

Strategies for improving choke usage include employing automatic choke systems and educating users about proper starting procedures for enhanced engine functionality and reduced environmental impact.

What Common Issues Can Prevent a Stihl MS 251 Chainsaw from Starting?

Common issues that can prevent a Stihl MS 251 chainsaw from starting include fuel problems, ignition system failures, and air filter obstructions.

Fuel problems
Ignition system failures
Air filter obstructions
Carburetor issues
Engine flooding
Chain brake engaged

Understanding these issues is essential for effective troubleshooting and maintenance of the chainsaw.

Fuel Problems:
Fuel problems often prevent a Stihl MS 251 chainsaw from starting. Stale fuel can clogged the fuel lines or cause the engine to run poorly. The manufacturer recommends using a fresh fuel mix every month. Mixing fuel in a proper ratio with the right oil is crucial. A 50:1 ratio of gasoline to two-cycle engine oil is typically used for Stihl chainsaws. Additionally, ensure the fuel tank is filled adequately and that there are no leaks.
Ignition System Failures:
Ignition system failures can also hinder a chainsaw from starting. A faulty spark plug can cause incomplete combustion. It is advisable to check the spark plug for wear, carbon buildup, or damage. Replacing the spark plug every season is a good maintenance practice. Tests should ensure that a strong spark is present when pulling the starter cord.
Air Filter Obstructions:
Air filter obstructions can impede engine air intake, affecting performance and startup. A clogged air filter reduces airflow and can cause the chainsaw not to start. Regularly cleaning or replacing the air filter is necessary to maintain optimal airflow. Be attentive to the manufacturer’s guidelines concerning air filter maintenance to ensure the device operates smoothly.
Carburetor Issues:
Carburetor issues can also affect chainsaw operation. If the carburetor gets clogged or out of adjustment, it can lead to fuel delivery problems. Using a carburetor cleaner can help resolve minor blockages. If problems persist, professional servicing may be required to correctly adjust or rebuild the carburetor.
Engine Flooding:
Engine flooding occurs when too much fuel enters the combustion chamber, preventing the engine from starting. Symptoms include a smell of gasoline after multiple start attempts. To address this, users should allow the chainsaw to sit for a few minutes to let excess fuel evaporate. Following this, the user should start with the choke in the correct position according to the operating instructions.
Chain Brake Engaged:
Engaging the chain brake on the Stihl MS 251 can inadvertently prevent it from starting. This safety feature is designed to protect the user. Ensure that the chain brake is disengaged prior to attempting to start the chainsaw. Following safety protocols guarantees not only the successful starting of the chainsaw but also helps in maintaining operational safety.

Why Won’t My Stihl MS 251 Chainsaw Start?

Your Stihl MS 251 chainsaw may not start due to several potential issues. Common causes include fuel problems, spark plug failure, or air filter obstructions. A thorough inspection can help identify and resolve the problem.

The Stihl manufacturer’s website provides definitions and troubleshooting tips for their equipment. They emphasize that proper fuel mixture and maintenance are critical for optimal performance and longevity.

Several underlying causes may prevent your chainsaw from starting. Firstly, if the fuel is stale or improperly mixed, it can lead to ignition failure. The Stihl MS 251 requires a specific fuel-to-oil ratio, typically 50:1. Secondly, a faulty spark plug can disrupt the ignition process. Lastly, a clogged air filter may restrict airflow, preventing combustion.

Technical terms like “fuel mixture” refer to the proper ratio of gasoline to oil required for two-stroke engines, like the one in your chainsaw. “Ignition” refers to the process of starting the engine by creating a spark to combust the fuel-air mixture. Understanding these terms can help clarify the issues at hand.

When the fuel is left unused for extended periods, it can deteriorate. This degradation affects combustion, which is the process of burning fuel to generate power. Additionally, if the spark plug is dirty or worn, it may fail to produce a spark. This lack of spark prevents the engine from starting. Similarly, a dirty air filter can block airflow, leading to a rich fuel mixture, which is when too much fuel is present relative to air.

Specific conditions contributing to starting issues may include environmental factors or improper storage. For instance, extreme temperatures can affect fuel and oil consistency. Storing fuel in a non-airtight container can lead to evaporation of volatile components, rendering it ineffective. Regular maintenance, including cleaning or replacing components like fuel filters and spark plugs, can mitigate these problems.

How Can Troubleshooting Help Identify Starting Problems?

Troubleshooting helps identify starting problems by systematically analyzing symptoms to uncover root causes. This approach is essential in pinpointing specific issues that prevent equipment, like a chainsaw, from starting.

Symptom recognition: Troubleshooting begins by identifying symptoms, such as unusual noises or failure to turn over. According to a study by Jones (2020), noting these symptoms can lead to more accurate diagnoses.
Process of elimination: Troubleshooting involves eliminating potential issues one by one. This includes checking fuel levels, inspecting spark plugs, and examining choke settings. Research from Smith and Kahn (2021) shows that a methodical approach can improve problem resolution times.
Use of tools: Technicians often use diagnostic tools, such as multimeters or compression gauges, when troubleshooting. These tools provide concrete data to support diagnoses. A study by Lee (2019) confirmed that using proper tools significantly enhances accuracy in identifying faults.
Understanding mechanics: A clear understanding of the equipment’s components aids in troubleshooting. Knowing how each part functions, such as the ignition system, contributes to identifying irregularities. According to Gonzalez (2022), knowledge of mechanics correlates with successful troubleshooting outcomes.
Documentation: Keeping a troubleshooting record helps in recognizing patterns of failure over time. This historical data can guide future interventions, streamlining the process. A report by Martin (2018) highlighted that well-documented service history led to quicker diagnostics in subsequent issues.

Through these steps, troubleshooting effectively narrows down the cause of starting problems, facilitating timely and accurate repairs.

What Maintenance Tips Improve the Start-Up Process of a Stihl MS 251 Chainsaw?

To improve the start-up process of a Stihl MS 251 chainsaw, perform regular maintenance and adhere to proper operational practices.

Clean the Air Filter
Inspect the Spark Plug
Use Fresh Fuel
Check the Fuel Filter
Ensure Proper Oil Levels
Lubricate Moving Parts
Store the Chainsaw Properly

These maintenance tips are essential for optimal performance. Each point contributes to the overall efficiency and reliability of the chainsaw’s start-up process.

Clean the Air Filter: Cleaning the air filter improves airflow to the engine. A clean air filter reduces dirt and debris, ensuring the engine receives the right amount of air for combustion. Sticking to a schedule of cleaning or replacing the air filter every 10 to 20 hours of operation enhances start-up reliability.
Inspect the Spark Plug: Inspecting the spark plug ensures proper ignition. A well-functioning spark plug ignites the fuel-air mixture efficiently. Replace it if it shows signs of wear, such as corrosion or a broken electrode. Regular checks every few months may prevent difficult start-ups due to poor ignition.
Use Fresh Fuel: Using fresh fuel is critical for optimal engine performance. Chainsaws require fuel mixed with oil for lubrication. Stale fuel can cause starting issues or engine knocking. Storing the fuel for no more than 30 days, and using fuel stabilizers for longer storage, will maintain engine efficiency.
Check the Fuel Filter: Checking the fuel filter prevents contamination from debris. A clogged fuel filter slows fuel flow to the engine, making starting difficult. Inspect and replace the filter as needed, generally every season or after heavy use, to ensure a smooth start-up.
Ensure Proper Oil Levels: Ensuring proper oil levels maintains chain lubrication and prevents overheating. A chainsaw operates best when the oil reservoir is filled before use. Check the oil level each time before starting the saw for optimal performance.
Lubricate Moving Parts: Lubricating moving parts reduces friction and wear. Regular application of appropriate lubricants ensures that the chainsaw operates smoothly. Focus on areas such as the bar and chain, and the pivot points to enhance lifespan and starting efficiency.
Store the Chainsaw Properly: Storing the chainsaw properly protects it from environmental damage. Keep it in a cool, dry place, and avoid prolonged exposure to moisture or extreme temperatures. Proper storage can prevent rust and ensure a reliable start every time.

By following these maintenance tips, users can ensure that their Stihl MS 251 chainsaw starts efficiently and operates effectively. Regular attention to these details can significantly enhance the overall user experience and performance of the equipment.

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