How To Start A Stihl MS 250 Chainsaw: A Step-by-Step Cold And Hot Starting Guide

Master the starting procedure of your Stihl MS 250 by engaging the chain brake, squeezing the throttle lockout to shift the Master Control Lever down to Full Choke, and pulling the starter rope until the engine ignites once. Immediately move the lever up to the Half-Choke (Warm Start) position, pull again to start the engine, and squeeze the throttle trigger to drop the saw into normal idle. This procedure ensures rapid ignition while preventing engine flooding and premature wear on the starter assembly.

To keep a Stihl MS 250 chainsaw running reliably for years, you must master its starting sequence and fuel requirements. The Stihl MS 250 is a powerhouse semi-professional chainsaw featuring a 45.4 cc engine. Because it relies on a manual choke and a specialized Master Control Lever, starting it incorrectly can quickly flood the engine or wear out the starter rope. This guide provides the exact mechanical steps, safety protocols, and troubleshooting workflows required to start your chainsaw safely and efficiently in any weather.

Pre-Operation Inspection & Safety Checklist

Before attempting to crank the engine, you must inspect the physical and mechanical integrity of the chainsaw. Operating a chainsaw with loose components, incorrect chain tension, or degraded fuel can cause catastrophic engine failure or severe physical injury.

Mandatory Operational Metrics & Equipment Checklist

• Estimated Prep Time: 5 to 10 minutes.
• Skill Level Required: Beginner to Intermediate.
• Personal Protective Equipment (PPE): Chainsaw chaps (meeting ASTM F1897 standards), heavy-duty leather gloves, safety glasses (ANSI Z87.1 certified), and hearing protection (NRR rating of 25 dB or higher).
• Fuel Requirements: Fresh mid-grade or premium unleaded gasoline (minimum 89 octane) with a maximum of 10% ethanol (E10), mixed at a precise 50:1 ratio with high-quality two-stroke air-cooled engine oil (such as Stihl HP Ultra or HP Super).
• Chain Tension Benchmark: The chain must fit snugly against the underside of the guide bar but still turn easily when pulled along the bar by a gloved hand. When tensioned correctly, you should be able to lift the drive links slightly out of the bar groove, but they should not fully disengage.

Step-by-Step Stihl MS 250 Starting Procedure

The Stihl MS 250 utilizes a single Master Control Lever on the rear handle to control the choke, throttle lock, and ignition switch. Understanding how this lever moves is essential. From top to bottom, the four positions on the lever are:

• Stop (0): Ignition circuit is broken; the engine stops running.
• Run (I): Normal operating position once the engine is warm.
• Warm Start (Start): Half-choke / part throttle used to restart a warm engine or to run the engine immediately after the first cold ignition "burp."
• Cold Start (Choke): Full-choke / closed carburetor flap used only when the engine is completely cold.

Step 1: Engage the Chain Brake

Place the chainsaw on a flat, stable surface clear of logs, brush, or rocks. Push the hand guard forward toward the guide bar with your left hand. You will hear a distinct click, confirming the chain brake is engaged. This mechanically locks the clutch drum, preventing the cutting chain from rotating on the bar during the starting process.

Warning: Never attempt to start the chainsaw with the chain brake disengaged. If the engine starts at high revs (which occurs naturally in the choke and warm start positions), the chain will spin instantly, creating an immediate laceration hazard.

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

Because the Master Control Lever is linked to the throttle assembly, you cannot slide it directly to the bottom Cold Start position from the Run position without using the throttle. Squeeze the throttle trigger lockout (on top of the rear handle) and the throttle trigger (on the bottom) simultaneously. While holding both triggers in, use your thumb to push the Master Control Lever all the way down to the Choke (bottom-most) position. Release the triggers, and the lever will remain locked in the Full Choke position.

Step 3: Secure the Chainsaw on Level Ground

Place your right foot inside the rear handle loop to anchor the saw firmly to the ground. Place your left hand on the front handlebar, locking your elbow straight to keep the saw from tilting or swaying. Ensure the guide bar and cutting chain are not touching the ground or any nearby obstructions.

Pro-Tip: Never "drop-start" a chainsaw. Drop-starting involves holding the starter rope in one hand and dropping the saw body with the other. This unstable motion causes the bar to swing wildly, often resulting in severe leg or arm injuries.

Step 4: Pull the Starter Rope to Locate the Compression Stroke

Grip the starter rope handle with your right hand. Pull the rope slowly outward until you feel a firm resistance. This resistance indicates the piston has reached the compression stroke in the cylinder. Once you feel this resistance, pull the starter rope quickly and vertically upward with a short, powerful stroke.

Do not pull the rope to its absolute physical limit, as this can snap the cord or shatter the recoil spring. Guide the rope back into the housing slowly rather than letting it snap back uncontrolled. Repeat this process up to 3 to 5 times until the engine fires briefly (often described as a brief "cough," "burp," or "pop") and then dies.

Step 5: Shift the Master Control Lever to Warm Start (Half Choke)

The moment the engine makes its initial firing sound, stop pulling the rope. Keeping the saw on the Full Choke position for any more pulls will saturate the combustion chamber with excess fuel, flooding the engine. Push the Master Control Lever up one notch to the Warm Start (Start) position. You do not need to squeeze the throttle trigger to make this adjustment; simply flick the lever upward with your thumb.

Step 6: Pull the Starter Rope Until the Engine Ignites

With the lever in the Warm Start position, pull the starter rope again. The engine should ignite and begin running within 1 to 3 pulls. Because the Warm Start setting applies partial throttle, the engine will run at high RPMs immediately upon starting.

Step 7: Tap the Throttle Trigger to Settle the Idle

Once the engine is running, immediately squeeze and release the throttle trigger with a quick "blip" of your finger. This action automatically releases the Master Control Lever from the Warm Start position and drops it into the normal Run (I) position. The engine speed will instantly drop to a quiet, steady idle, and the clutch will disengage.

Step 8: Disengage the Chain Brake and Begin Cutting

Let the engine idle for 30 to 60 seconds to warm up the cylinder and distribute oil throughout the crankcase. To begin cutting, lift the chainsaw, grip both handles firmly, and pull the hand guard back toward the front handle with your left hand to disengage the chain brake. The chain is now free to spin when you squeeze the throttle.

Technical Specifications and Fuel Mixture Formulas

To maintain optimal combustion chamber temperatures and prevent piston scoring, the Stihl MS 250 must be operated according to its precise engineering tolerances. The following table highlights the critical engine and maintenance parameters for this specific model.

Troubleshooting Common Stihl MS 250 Starting Failures

If your chainsaw fails to start after following the standard starting sequence, you are likely dealing with a flooded engine, fuel starvation, or a fouled spark plug. Use the following diagnostic steps to resolve these common issues.

Scenario 1: The Engine is Flooded

This occurs when the starter rope is pulled too many times on the Full Choke setting, saturating the spark plug electrodes in raw fuel and preventing ignition.

• Root Cause: Excess fuel in the combustion chamber blocks the spark plug from generating a combustible arc.
• Actionable Fix: Flip the Master Control Lever to the Stop (0) position. Use the spark plug wrench (scrench) to remove the top orange engine cover and unscrew the spark plug. If the plug tip is wet with fuel, wipe it dry with a clean shop towel or blow it clean with compressed air. With the spark plug removed, set the saw on the ground, turn it on its side (spark plug hole facing down), and pull the starter rope rapidly 15 to 20 times to blow excess fuel out of the cylinder. Reinstall the dry spark plug, tighten it to 20 Nm (14.8 ft-lbs), and set the Master Control Lever to the Run (I) or Warm Start position (with no choke). Pull the starter rope until the engine fires and clears the remaining vapor.

Scenario 2: The Engine Starts but Dies Instantly When Squeezing the Throttle

The engine fires but bogs down, sputters, and stalls the moment you touch the throttle trigger to transition into the Run position.

• Root Cause: The engine temperature is too low to vaporize the fuel-air mixture without the choke restrictor plate engaged, or there is an air leak in the carburetor intake boot.
• Actionable Fix: Allow the saw to run in the Warm Start position for a longer duration (10 to 15 seconds) before blipping the throttle. This allows the cylinder wall to warm up, facilitating proper fuel vaporization. If the issue persists, locate the carburetor adjustment screws on the right side of the saw. Turn the Low-speed mixture screw (L) counterclockwise by 1/8th of a turn to richen the idle fuel mixture, preventing stalling during transitions.

Scenario 3: The Starter Rope is Hard to Pull or Jammed

The starter rope resists movement or feels physically locked, preventing you from cranking the engine.

• Root Cause: Hydrostatic lock (liquid fuel filling the combustion chamber) or a broken recoil starter spring/pawl assembly.
• Actionable Fix: Remove the spark plug and attempt to pull the rope. If the engine spins freely, the issue is hydrostatic lock; clear the fuel from the cylinder as outlined in Scenario 1. If the rope remains stuck with the spark plug removed, unscrew the four housing screws securing the starter cover on the left side of the saw. Inspect the polymer starter pawls and return spring for breaks, dirt, or binding. Clean the assembly with a degreaser or replace a broken recoil spring.

Frequently Asked Questions

Why is my Stihl MS 250 so difficult to start after sitting for a few weeks?

Two-stroke fuel begins to degrade in as little as 30 days, causing the volatile lighter compounds of the gasoline to evaporate. This leaves behind a sticky, varnish-like residue that clogs the tiny passages in the carburetor's jet system. To prevent this, always drain the fuel tank or run the saw dry before storage, or use a fuel stabilizer like Stihl MotoMix.

How do I start a warm Stihl MS 250 chainsaw that was recently used?

To start a warm engine, do not use the Full Choke setting. Instead, lock the Master Control Lever into the Warm Start (Start) position, secure the saw on the ground, and pull the starter rope. The engine should fire on the first or second pull. Once it starts, quickly squeeze the throttle to drop the lever into the Run (I) position.

What spark plug gap is required for the Stihl MS 250?

The spark plug electrode gap must be set to exactly 0.5 mm (0.020 inches) using a spark plug gapping tool. An incorrect gap will result in weak ignition spark, causing hard starting, rough idling, and incomplete fuel combustion.

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

If the chain spins at idle, your idle speed is set too high or the clutch springs are worn out and failing to retract the clutch shoes. Adjust the idle speed screw (LA) on the side of the carburetor counterclockwise until the chain stops moving at idle. If the chain continues to spin, inspect the clutch assembly for broken springs.

Maintain Your Chainsaw for Reliable Starts

Keep your Stihl MS 250 running at peak performance by pairing proper starting techniques with premium maintenance habits. By utilizing clean fuel, cleaning the air filter every five tanks of fuel, and following these safe starting protocols, your chainsaw will start reliably on every job.