Starting a Stihl MS250 chainsaw involves a clear, step-by-step process for both cold and warm engines. If your saw won’t start, you must check the fuel mix, spark plug, and air filter first. This guide will walk you through every step to get your reliable Stihl running smoothly.
Preparing Your Stihl MS250 for First Use
Before you can start the saw, you need to set it up correctly. This initial setup is vital for safety and performance. If you just bought a new saw, follow the steps in the assembling Stihl MS250 saw section carefully.
Safety First: Gear Up
Never start the saw without proper safety gear. Chainsaws are powerful tools.
- Wear a helmet with a face screen.
- Use safety glasses or goggles.
- Put on ear protection.
- Wear cut-resistant gloves and boots.
- Wear snug-fitting, durable clothing.
Bar and Chain Setup
The bar and chain must be correctly attached and tensioned. Refer to your Stihl MS250 manual for specific torque settings, but here is the general process for Stihl MS250 chain tensioning:
- Ensure the bar nut is loose.
- Use the combination wrench to turn the bar nut a little at a time.
- Check the chain tension often. The chain should be snug against the bottom of the guide bar.
- When you pull the chain down, the drive links should just clear the bottom groove of the bar.
- Tighten the bar nut firmly.
Fuel Mixture Essentials
The MS250 is a two-stroke engine. It needs a specific mix of gasoline and two-cycle oil. Using the wrong mix can destroy the engine quickly. This is a key part of any good Stihl MS250 maintenance guide.
The correct Stihl MS250 oil mix ratio is 50:1.
Table 1: Fuel Mix Guide for Stihl MS250 (50:1 Ratio)
| Component | Amount |
|---|---|
| Premium Unleaded Gas | 1 Gallon (or 1 liter) |
| Stihl 2-Cycle Engine Oil | 2.6 Ounces (or 20 milliliters) |
Always use high-quality, fresh fuel. Never use old gas or engine oil meant for cars. Mix the fuel in a clean container approved for gasoline.
Priming the Engine
The primer bulb moves fuel from the tank to the carburetor.
- Locate the primer bulb near the fuel cap.
- Press the bulb slowly three to five times.
- Watch the bulb; you should see fuel flow into the clear section of the bulb.
- Stop when you see fuel move. Do not over-prime.
Step-by-Step Guide: Starting a Cold Stihl MS250
Starting a cold Stihl MS250 requires using the choke. The choke restricts airflow. This makes the fuel mixture richer, which helps the cold engine fire up.
Step 1: Engage the Choke
- Move the Master Control Lever (usually a switch near the throttle handle) down to the ‘Cold Start’ or ‘Choke’ position (often marked with a symbol like a solid square or “I”).
- If the engine is flooded later, you will move this lever to the top position (‘Stop’ or ‘0’).
Step 2: Set the Throttle Latch (Half-Throttle Lock)
- Press the throttle trigger halfway in.
- Push the Master Control Lever up to lock it in place. This engages the fast idle setting. This keeps the engine running when it first starts before you fully open the throttle.
Step 3: Use the Decompression Valve (If Equipped)
Some MS250 models have a decompression valve. This makes pulling the starter rope easier.
- Locate the small button on the cylinder head.
- Push this button in before you pull the rope.
- Pull the rope a few times with the decompression valve open. This clears any excess compression.
- Close the decompression valve just before the final starting pull.
Step 4: Pull the Starter Rope
- Place the saw on firm, level ground.
- Grip the starter handle firmly with one hand.
- Keep the saw body steady with your other hand holding the front handle. Do not wrap the rope around your hand.
- Pull the starter rope sharply and quickly, using a full arm extension. Do not let the rope snap back; guide it gently back into the housing.
The engine should sputter or briefly fire.
Step 5: Disengage the Choke
Once the engine sputters once or twice:
- Move the Master Control Lever up from the choke position to the run position (usually marked with a “Run” or “II”). This turns the choke off.
- The throttle lock should disengage automatically.
Step 6: Final Start
- Give the starter rope one more sharp pull.
- The saw should now start and idle. If it runs, let it warm up for a minute.
Starting a Warm Stihl MS250
A warm engine does not need the full choke. This is where many beginners make mistakes and flood the engine.
- Move the Master Control Lever to the ‘Run’ position (no choke).
- If the saw was running just a few minutes ago, you may not need to press the primer bulb.
- Pull the starter rope sharply. The engine should start quickly.
If it still needs a little help, you can briefly use the primer bulb once or twice, but avoid using the full choke setting.
Stopping the Saw
To stop the saw, simply move the Master Control Lever all the way to the ‘Stop’ position (marked with ‘0’ or ‘Stop’). This cuts the ignition.
Advanced Operation: Carburetor Fine-Tuning
Sometimes, even after following the steps above, the saw runs poorly. This might require MS250 carburetor adjustment. Adjustments should only be made when the saw is warm and running. Always refer to the Stihl MS250 manual for exact starting points for these screws.
The carburetor has three main adjustment screws:
- L (Low Speed): Controls fuel mixture at idle.
- H (High Speed): Controls fuel mixture at wide-open throttle.
- LA (Idle Speed/Throttle Stop): Sets how fast the engine idles when the throttle is not pressed.
General Adjustment Procedure:
- Set Idle Speed (LA): Adjust this screw until the saw idles smoothly without the chain spinning. If the chain spins, turn the LA screw clockwise (in) slightly.
- Set High Speed (H): Adjust the H screw until the engine reaches its highest RPM without sounding like it is struggling or four-stroking. Turn clockwise to lean the mixture (less fuel) or counter-clockwise to enrich it (more fuel).
- Set Low Speed (L): With the H screw set, slowly increase the throttle to mid-range, then back down. Adjust the L screw for smooth transition between idle and high speed.
- Final Check: Check the high speed again. The transition from low to high speed must be clean.
Caution: Improper MS250 carburetor adjustment can lead to engine damage, overheating, or poor cutting performance. If you are unsure, take the saw to an authorized dealer.
Routine Checks and Maintenance
Regular checks keep the MS250 starting easily every time. A comprehensive Stihl MS250 maintenance guide covers more than just starting.
Checking Spark Plug Health
A fouled or weak spark plug is a common reason for starting difficulty. Stihl MS250 spark plug replacement is simple maintenance.
- Ensure the saw is off and cool.
- Remove the cylinder cover.
- Use the correct spark plug wrench (usually part of the combination tool) to unscrew the old plug.
- Inspect the gap. Stihl typically recommends a gap of about 0.030 inches (0.75 mm) for the MS250. Check your manual.
- Install a new, correct spark plug (e.g., NGK BPMR7A). Tighten snugly, but do not overtighten.
Air Filter Inspection
A clogged air filter suffocates the engine, making it hard to start or causing it to run poorly even when running.
- Remove the top cover.
- Remove the air filter element.
- If it is a mesh filter, clean it with warm, soapy water and let it dry completely before reinstalling.
- If it is a fleece or felt filter, gently tap out the debris or use low-pressure compressed air blowing from the inside out. Replace if heavily soiled.
Bar and Chain Oil
While not directly related to starting, if the chain oil tank is empty, the saw may hesitate, or you might not want to run it long enough for it to fully start. Always top up the bar and chain oil reservoir with quality Stihl bar oil.
Troubleshooting Common MS250 Starting Issues
If your saw refuses to start after several attempts, follow this troubleshooting flow. This section aids in Stihl 250 troubleshooting.
Table 2: Stihl MS250 Troubleshooting Guide
| Symptom | Likely Cause(s) | Quick Fixes |
|---|---|---|
| Engine pulls but never fires. | No fuel reaching the cylinder; Incorrect choke setting. | Check fuel level. Ensure primer bulb is pressed. If cold, use full choke. If warm, use no choke. |
| Engine sputters and dies immediately. | Choke left on; Fuel mixture too rich (flooded). | Move choke to run position immediately after sputter. Pull rope 10–12 times with choke OFF to clear flood. |
| Engine starts but runs very rough or stalls under load. | Dirty carburetor; Incorrect high-speed setting; Bad spark plug. | Perform MS250 carburetor adjustment. Replace the Stihl MS250 spark plug replacement. |
| Engine pulls very hard (difficult starting). | Decompression valve stuck closed (if equipped); Spark plug fouled or too tight. | Open decompression valve fully. Check spark plug tightness and condition. |
| Engine smokes heavily and smells of fuel. | Flooded engine. | Remove spark plug. Pull rope 5 times with the plug out to clear excess fuel. Let dry for 15 minutes. |
Dealing with a Flooded Engine
Flooding occurs when too much fuel enters the cylinder, usually by pulling the starter rope too many times while the choke is engaged.
- Set the Master Control Lever to the STOP (0) position.
- Remove the spark plug.
- Pull the starter rope about 8-10 times. This forces the excess fuel out of the cylinder through the spark plug hole.
- Leave the spark plug out for 10 minutes to let the excess fuel evaporate.
- Reinstall the spark plug, ensuring it is clean and gapped correctly.
- Attempt to start using the Warm Start Procedure (choke off).
Fuel System Deep Dive
Fuel issues are the number one reason chainsaws fail to start. Always use fresh fuel, ideally mixed no more than 30 days prior. Stihl sells high-quality pre-mixed fuel (Stihl MotoMix) which lasts much longer and simplifies the process, especially avoiding the Stihl MS250 oil mix ratio calculation errors.
If the saw sat over winter with old fuel, you must drain the tank and carburetor bowl. Old fuel gums up the tiny passages in the carburetor. This leads directly to starting problems that simple adjustments cannot fix, requiring professional carburetor cleaning or replacement, often detailed in sections of the Stihl MS250 manual concerning long-term storage.
The Role of the Starter Rope and Recoil Spring
The starter rope assembly transfers your pull energy to the engine’s flywheel. If the rope feels weak or doesn’t retract properly, it affects your ability to spin the engine fast enough to achieve ignition.
- If the rope retracts slowly, the recoil spring may need adjustment or replacement.
- If the rope pulls out fully but doesn’t engage the engine, the pawls inside the recoil housing might be worn or stuck.
These repairs are more involved and usually require consulting a technician or deeply diving into the more complex sections of the Stihl MS250 manual.
Final Checks Before Each Use
Always perform these quick checks before attempting the Stihl 250 chainsaw startup:
- Is the chain properly tensioned (Stihl MS250 chain tensioning)?
- Is the chain brake engaged for starting? (Push forward toward the bar tip).
- Is the fuel mixture correct (Stihl MS250 oil mix ratio)?
- Is the air filter clean?
By meticulously following the preparation steps, using the correct choke setting for the temperature, and performing basic checks, you will master starting your Stihl MS250 quickly and reliably. Remember that consistency in your starting routine is key to avoiding common pitfalls like flooding the engine.
Frequently Asked Questions (FAQ) About Starting the Stihl MS250
Q: Why does my Stihl MS250 start fine when cold but die when I try to restart it warm?
A: This almost always means you are accidentally engaging the choke when restarting a warm engine. A warm engine needs the choke fully OFF (Run position). If it still stalls, the carburetor might be running too rich at the high-speed setting, requiring a slight MS250 carburetor adjustment on the H screw (lean it out slightly).
Q: Can I use regular unleaded gas in my Stihl MS250?
A: Yes, you can use regular unleaded gasoline (89 octane or higher is recommended), but you absolutely must mix it with high-quality, Stihl MS250 oil mix ratio-approved two-cycle oil at 50:1. Never use straight gasoline.
Q: How often should I check the Stihl MS250 spark plug replacement interval?
A: For heavy use, check the spark plug condition every 50 operating hours or at least once per cutting season. A good sign it needs attention is difficulty starting, rough running, or poor throttle response.
Q: My saw is sputtering but won’t fully catch. What should I check next after the choke procedure?
A: If the sputter is weak, check the fuel flow by pressing the primer bulb several times—is fuel moving? If fuel is moving, the next step in Stihl 250 troubleshooting is checking the spark plug condition and gap. A weak spark means ignition failure.
Q: I just finished assembling Stihl MS250 saw. Do I need to adjust the idle screw right away?
A: Not usually. The saw should be reasonably close from the factory. Only adjust the idle screw (LA) if the chain spins while the engine is idling, or if the engine stalls frequently when you let off the throttle quickly. Always check the Stihl MS250 manual first.