How To Start A Stihl MS250: The Complete Operator Guide
Starting a Stihl MS250 chainsaw requires a precise sequence of fuel management, master control lever adjustments, and proper pull-cord technique to prevent engine flooding. Mastering this process ensures reliable ignition for the 45.4 cc two-stroke engine while protecting the recoil starter assembly from premature wear.
Pre-Operation & Safety Preparation Checklist
Before attempting to start your Stihl MS250, you must establish a safe workspace and verify that the equipment is mechanically prepared to run. Operating a 3.0-horsepower chainsaw demands rigorous attention to safety protocols and fluid parameters to prevent kickback, engine overheating, or fuel starvation.
- Essential Gear and Materials:
- Stihl 2-stroke engine oil mixed at a 50:1 ratio with fresh unleaded gasoline (minimum 89 octane).
- Stihl chain lubricant oil for the bar and chain reservoir.
- Personal protective equipment including ANSI-rated eye protection, chainsaw chaps, heavy-duty work gloves, steel-toe boots, and hearing protection.
- Combination wrench (scrench) for spark plug and tension adjustments.
- Prerequisite Knowledge and Standards:
- Familiarity with the chain brake mechanism and its dual-action safety features.
- Understanding of standard two-stroke carburetion behavior (choke, half-throttle, run positions).
- Completion of a pre-flight inspection covering the air filter, chain tension, and bar groove cleanliness.
- Time and Scope Benchmarks:
- Estimated setup and startup time: 3 to 5 minutes.
- Operating environment: Clear, stable ground at least 10 feet away from the fueling location.
Step-by-Step Procedure for Starting Your Stihl MS250
Step 1: Fuel and Chain Oil Inspection
Inspect the fuel and oil tanks before every operational session. Unscrew the filler caps and verify that the fuel tank contains a fresh 50:1 mixture of high-octane gasoline and high-grade two-stroke oil. Fill the chain oil reservoir with bar and chain oil, ensuring the fluid level remains visible through the translucent window. Securely tighten both caps to prevent vacuum locks or leakage during operation.
Warning: Never fuel a chainsaw within 10 feet of open flames, sparks, or a hot engine. Wipe away any spilled fuel immediately before attempting ignition.
Step 2: Engage the Chain Brake
Push the front hand guard forward toward the guide bar until you hear a distinct click. This engages the chain brake, locking the clutch drum and stopping the chain from rotating during the starting sequence. Never attempt to start the chainsaw with the chain brake disengaged, as a fast-spinning chain poses severe safety hazards.
Step 3: Set the Master Control Lever
Locate the Master Control Lever on the rear handle. Depress the throttle trigger interlock and squeeze the throttle trigger while simultaneously pushing the Master Control Lever all the way down to the full choke position. This setting closes the choke valve, enriches the air-fuel mixture for a cold start, and fast-idles the throttle.
Pro-Tip: If the engine is already warm from recent operation, skip the full choke position and push the Master Control Lever to the warm start or half-throttle position to prevent immediate engine flooding.
Step 4: Stabilize and Secure the Saw
Place the chainsaw on a firm, flat surface outdoors. Insert your right foot into the rear handle opening to anchor the saw securely to the ground. Place your left hand firmly on the front handlebar wrap, keeping your arm straight and your elbow locked. Ensure the guide bar and chain are completely clear of foreign objects, dirt, and your own body.
Step 5: Pull the Starter Cord
Grip the starter grip with your right hand and pull the starter rope slowly outward until you feel distinct resistance as the piston reaches compression. Without letting the starter grip snap back against the housing, pull the rope firmly and rapidly upward in a controlled, vertical motion. Repeat this until the engine attempts to fire or "coughs" once, which indicates the initial combustion cycle.
Step 6: Transition to Fast Idle and Start
As soon as the engine fires and dies or stumbles (usually within 1 to 3 pulls on full choke), immediately move the Master Control Lever up one notch to the warm start or half-throttle position. Anchor the saw securely once again and pull the starter rope briskly until the engine starts and runs smoothly. Once running, blip the throttle trigger quickly with your index finger; the Master Control Lever will automatically snap upward into the standard run position, dropping the engine into a steady idle.
Recoil Pull Start Starter For STIHL 1123 080 1802 MS250 MS230 MS210 023 ...
Technical Specifications and Operating Parameters of the Stihl MS250
| Technical Parameter | Specification Value | Operational Impact |
|---|---|---|
| Displacement | 45.4 cc (2.77 cu. in.) | Delivers high torque and cutting speed for medium-duty limbing and bucking. |
| Power Output | 2.2 kW (3.0 bhp) | Powers through hardwoods up to 14 inches in diameter with minimal bogging. |
| Fuel Mixture Ratio | 50:1 (Gasoline to Oil) | Prevents piston scoring and cylinder wall scuffing under high thermal loads. |
| Spark Plug Type | Bosch WSR 6 F or NGK BPMR7A | Maintains consistent electrical spark gap (0.5 mm / 0.020 in.) for clean ignition. |
| Dry Weight | 4.6 kg (10.1 lbs) | Minimizes operator fatigue during extended bucking and felling tasks. |
Troubleshooting Common Starting Failures and Field Fixes
Even with correct procedure, two-stroke engines can experience starting hurdles due to weather, fuel degradation, or ignition fouling. Apply these targeted field fixes to restore normal operation quickly.
- Symptom: Engine floods with raw fuel after excessive pulls on full choke.
- Root Cause: Excessive fuel has pooled inside the combustion chamber and wet-fouled the spark plug electrode, preventing electrical spark.
- Actionable Fix: Move the Master Control Lever to the off position, remove the spark plug using your scrench, and invert the chainsaw to drain excess fuel from the cylinder. Pull the starter cord briskly 5 to 6 times to clear the crankcase. Dry and reinstall the spark plug, set the lever to the run position (no choke), and pull the cord to restart.
- Symptom: Starter rope pulls freely with no engine resistance or compression.
- Root Cause: A sheared flywheel key, stuck piston rings, or a loose spark plug causing loss of cylinder compression.
- Actionable Fix: Check that the spark plug is tightened to the correct torque specification. If compression remains absent, inspect the cylinder wall and piston through the exhaust port for scoring, or verify the starter pawls are engaging the flywheel properly.
- Symptom: Saw starts briefly on choke, then dies immediately when throttle is applied.
- Root Cause: The carburetor mixture screws are set too lean, or stale fuel has varnished the idle jets.
- Actionable Fix: Allow the engine to warm up for 60 seconds on half-throttle. If it stalls upon acceleration, drain the fuel tank, flush with fresh 50:1 mixture, and adjust the low-speed (L) carburetor jet counter-clockwise by 1/8 to 1/4 turn to enrich the idle circuit.
Frequently Asked Questions
What fuel ratio should I use in a Stihl MS250?
You must use a strict 50:1 fuel-to-oil ratio, combining fresh unleaded gasoline with a minimum 89 octane rating and high-quality Stihl two-stroke air-cooled engine oil. Using unmixed straight gasoline will permanently seize the engine within minutes of operation.
Why does my Stihl MS250 pull cord feel stuck or hard to pull?
A stuck pull cord usually indicates that the engine is flooded with fuel behind the piston, creating hydraulic lock, or the chain brake is disengaged while the clutch is jammed. Clear any potential flood condition by removing the spark plug, clearing the cylinder, and verifying the chain brake is fully engaged before pulling.
How often should I replace the spark plug on an MS250?
Inspect the spark plug every 100 hours of operation or annually, cleaning carbon deposits off the electrode with a wire brush. Replace the spark plug entirely if the electrode shows excessive wear, heavy pitting, or if the ceramic insulator cracks.
Can I start a Stihl MS250 using the drop-start method?
No, drop-starting—holding the rear handle with one hand and pulling the starter cord while dropping the saw—is strictly prohibited by Stihl safety guidelines. Always start the saw on a flat surface with your foot securely inside the rear handle and your left hand gripping the front handlebar.
What should I do if the saw won't start after sitting all winter?
Old fuel degrades quickly and forms varnish deposits that clog carburetor jets. Drain the fuel tank completely, clean or replace the fuel filter, fill the tank with fresh 50:1 fuel, and inspect the air filter before attempting the standard cold-start procedure.
