How To Start A STIHL 250 Chainsaw: Step-by-Step Ignition Guide

To start a STIHL MS 250 chainsaw, first engage the chain brake, depress the throttle trigger lockout, and move the Master Control Lever all the way down to the Full Choke position. Pull the starter rope until the engine briefly fires (or "coughs"), then move the lever up one notch to the Half-Throttle (Starting Throttle) position and pull again until the engine runs. Immediately squeeze and release the throttle trigger to drop the chainsaw into its normal idle speed.

Pre-Operation Checklist and Safety Requirements

Starting a powerful two-stroke engine like the STIHL MS 250 requires careful physical preparation and an understanding of the machine's mechanical state. Skipping safety precautions or using improper fuel mixtures can lead to severe personal injury, engine damage, or premature wear of the clutch assembly. Before pulling the starter rope, ensure you satisfy all mechanical and environmental safety requirements.

Essential Gear and Safety Equipment

• Personal Protective Equipment (PPE): Heavy-duty work gloves, ANSI-approved eye protection, hearing protection (earmuffs or plugs rated for at least 85 dB), chainsaw chaps, and steel-toe boots with high-traction soles.
• Fresh Fuel Mixture: A precise 50:1 ratio of fresh, mid-grade unleaded gasoline (minimum 89 octane with no more than 10% ethanol) and high-quality two-stroke air-cooled engine oil.
• Bar and Chain Lubricant: High-viscosity bar and chain oil filled to capacity.
• Clear Operating Space: A 10-foot clearing on flat, stable ground, free of sticks, gravel, spectators, and flammable debris.

Pre-Flight Mechanical Inspection

1. Check Chain Tension: The saw chain should sit snugly against the underside of the guide bar but still be easily rotated by a gloved hand.
2. Inspect Lubricant Levels: Fill both the fuel and bar oil reservoirs. The bar oil reservoir should always be replenished every time you refuel.
3. Inspect the Spark Plug Boot: Ensure the black rubber boot is seated firmly on the terminal of the spark plug to prevent intermittent spark connection or ignition failure.

Detailed Step-by-Step Starting Procedure for the STIHL MS 250

The STIHL MS 250 features a integrated Master Control Lever that governs the choke flap, throttle latch, and short-circuit ignition switch. Understanding how to manipulate this lever is the key to reliable starting.

Step 1: Engage the Chain Brake

Push the hand guard (the black lever in front of the handlebar) forward away from the handlebar. You will hear a distinct metallic click. This locks the clutch drum, preventing the saw chain from spinning around the guide bar when the engine ignites.

Warning: Never attempt to start the chainsaw without the chain brake engaged. Upon starting, the engine runs at half-throttle speed, and an unrestrained chain can cause immediate injury.

Step 2: Set the Master Control Lever to Full Choke (Cold Start)

The Master Control Lever is located on the rear handle's left side. To move it to the bottom-most position (Full Choke), you must first release the mechanical interlock. Press down on the throttle trigger lockout (the long lever on top of the rear handle), squeeze the throttle trigger (underneath the handle), and then push the Master Control Lever all the way down.

This mechanical sequence closes the choke flap to restrict airflow, enriching the fuel-to-air ratio needed for a cold engine block.

Step 3: Secure the Chainsaw on Level Ground

Place the chainsaw flat on a cleared patch of ground. Ensure the cutting attachment (bar and chain) does not touch any twigs, rocks, or the ground surface.

• Place your right foot firmly through the rear handle opening to anchor the back of the saw.
• Grasp the front handlebar firmly with your left hand, locking your elbow straight. This dual-point contact provides absolute control over the machine during the pull stroke.

Step 4: Pull the Starter Rope to Achieve the Engine "Cough"

With your right hand, grip the starter rope handle. Pull the rope slowly outward until you feel a firm resistance (this is the engine's compression stroke). Once you feel resistance, pull the rope quickly and vertically upward with a smooth, powerful motion.

Do not let the starter rope snap back violently; guide it back into the fan housing slowly so the recoil spring can wind correctly. Repeat this pull until the engine ignites briefly with a distinct "cough" or "burp" sound and then dies. This typically takes 2 to 5 pulls.

Pro-Tip: Stop pulling the rope in the Full Choke position as soon as you hear this brief ignition. Pulling the rope more than 5 times in Full Choke will flood the combustion chamber with excess fuel, rendering the engine temporarily unstartable.

Step 5: Shift to the Half-Throttle (Starting Throttle) Position

Once you hear the engine cough, move the Master Control Lever up one notch to the half-throttle position (indicated by a starting symbol). You do not need to depress the throttle trigger to move the lever up to this position. Moving the lever opens the choke flap, allowing air to mix with the fuel while keeping the idle speed mechanically elevated.

Step 6: Pull to Start and Run the Engine

With the saw securely anchored, pull the starter rope again using the same firm, vertical motion. The engine should ignite within 1 to 3 pulls and run at a high idle speed. The chain will not spin if the chain brake is engaged correctly.

Step 7: Blip the Throttle to Set the Saw to Normal Idle

Immediately after the engine starts, briefly squeeze (or "blip") the throttle trigger on the rear handle. This action automatically releases the Master Control Lever from the half-throttle setting and pops it up to the normal Run position (indicated by the "I" symbol). The engine speed will drop to a smooth, low idle, and the clutch will disengage.

Step 8: Disengage the Chain Brake and Begin Operation

Pull the front hand guard back toward the front handlebar until it clicks. The chain is now free to spin. Give the throttle trigger a quick squeeze to verify the chain moves smoothly over the bar and that oil is spraying from the automatic oiler onto a light background (like a clean stump or piece of cardboard).

Operating a Warm Engine (Warm Start Procedure)

If you have already run the engine, it is warm, or has only been shut off for a short period, you do not need to use the choke.

1. Engage the chain brake by pushing the hand guard forward.
2. Press the throttle trigger lockout and the throttle trigger, then push the Master Control Lever down past the Run position to the Start/Half-Throttle position. (Do not go down to Full Choke).
3. Place the saw securely on the ground.
4. Pull the starter rope until the engine fires and runs.
5. Quickly blip the throttle trigger to return the Master Control Lever to the normal Run position.

STIHL MS 250 Technical Specifications Reference

Understanding the mechanical tolerances and fuel properties of your MS 250 ensures long-term reliability and peak performance out of the 45.4 cc engine.

Troubleshooting Starting Failures and Engine Flooding

When a STIHL MS 250 fails to start, the issue is almost always related to fuel delivery, spark generation, or physical compression. Below are the most common mechanical roadblocks and how to resolve them.

Scenario A: The Engine is Flooded with Fuel

• Root Cause: The starter rope was pulled too many times while the Master Control Lever was in the Full Choke position, soaking the spark plug electrode in wet fuel and preventing ignition.
• Actionable Fix: Turn the Master Control Lever to the Stop ("0") position. Pull the spark plug boot off, and use a 19 mm spark plug wrench to unscrew and remove the spark plug. If the electrode is wet, wipe it dry with a clean cloth or blow it clear with compressed air. With the spark plug removed, tip the chainsaw upside down so the spark plug hole faces the ground. Pull the starter rope 15 to 20 times to clear excess fuel from the combustion chamber. Reinstall the dry spark plug, torque it down firmly, replace the boot, and attempt to start the saw with the Master Control Lever set directly to the Half-Throttle/Start position (no choke).

Scenario B: The Starter Rope is Hard to Pull or Seized

• Root Cause: Hydraulic lock due to extreme cylinder flooding, a jammed sprocket, or a seized starter recoil assembly.
• Actionable Fix: Remove the clutch cover and ensure the chain can move freely along the bar. If it is free, remove the spark plug as detailed in Scenario A and pull the starter rope. If the rope pulls smoothly with the plug removed, the issue was hydraulic lock from fuel. If it remains locked or stiff, remove the four screws holding the starter housing assembly to the side of the saw to inspect the recoil pulley for cracks, tangled rope, or a broken rewind spring.

Scenario C: The Engine Starts but Dies Instantly

• Root Cause: Fuel starvation due to a clogged fuel filter, a split fuel line, or an improperly adjusted carburetor low-speed (L) screw.
• Actionable Fix: Inspect the fuel filter inside the gas tank using a bent piece of wire to hook the fuel line and pull it out of the filler neck. If the filter is dark or clogged, replace it. If the filter is clean, locate the three carburetor adjustment screws on the right side of the shroud (marked H, L, and LA). Gently turn the Low-Speed screw (L) clockwise until it seats, then back it out exactly 1 full turn. Turn the Idle Speed screw (LA) clockwise until the throttle lever just begins to open, then back it off 1/4 turn to establish a baseline idle mixture.

Frequently Asked Questions

Why is my STIHL MS 250 hard to start when cold?

Cold starting difficulties are usually caused by stale fuel containing ethanol, which absorbs moisture from the air and restricts fuel flow through the tiny jets of the carburetor. To prevent this, use non-ethanol fuel paired with a fuel stabilizer, and ensure you push the Master Control Lever all the way down to the Full Choke position before your initial pulls.

What is the exact fuel-to-oil mix ratio for a STIHL MS 250?

The STIHL MS 250 requires a precise 50:1 ratio of gasoline to two-stroke engine oil. To achieve this, mix 2.6 fluid ounces of high-quality two-stroke engine oil with 1 gallon of mid-grade or premium unleaded gasoline (minimum 89 octane).

Why does my chainsaw chain spin when the engine is idling?

If the chain spins while the saw is idling and the chain brake is disengaged, your idle speed (LA screw) is set too high, or you have a broken clutch spring. Use a small screwdriver to turn the LA screw counterclockwise until the chain stops moving. If adjusting the screw has no effect, inspect the centrifugal clutch for broken tension springs.

How often should I clean or replace the spark plug on my MS 250?

You should inspect the spark plug every 10 to 15 operating hours for carbon buildup, scoring, or electrode wear. Clean the electrode with a wire brush, check that the gap is set to exactly 0.5 mm (0.020 in.), and replace the plug entirely after 100 hours of use or once per cutting season.

Maintain Your STIHL Chainsaw for Peak Cutting Power

Keep your chainsaw running smoothly by always using fresh, stabilized fuel and keeping the air filter clear of sawdust and oil residue. For specialized replacement components or complex carburetor adjustments, always consult an authorized STIHL servicing dealer to guarantee safety and protect your equipment's warranty.