Chainsaw Hard To Pull With Spark Plug In (3 Fixes For Stihl 025)

Chainsaw Hard to Pull with Spark Plug In: 3 Fixes for Stihl 025

I’ve spent a good portion of my life around chainsaws. My grandfather was a logger, and I practically grew up in the woods. I remember countless hours spent learning the ins and outs of different saws, from the hefty, older models to the more modern, lightweight ones. I’ve wrestled with my fair share of stubborn engines, and a common problem I’ve encountered, especially with Stihl 025s, is that frustratingly hard-to-pull starter cord when the spark plug is in. It feels like you’re trying to start a truck engine with a shoelace! This guide will walk you through the most likely causes and provide clear, step-by-step fixes.

Why is This Important?

A chainsaw that’s hard to pull isn’t just annoying; it can be dangerous. You’re more likely to strain your back or pull a muscle trying to get it started. More importantly, it’s a sign that something is wrong, and ignoring it can lead to further damage to your saw. For those of us who rely on chainsaws for everything from felling trees for firewood to trimming branches, a reliable starting saw is essential. Furthermore, understanding how to diagnose and fix this problem yourself can save you time and money on repairs.

Understanding the Basics: Compression, Fuel, and Spark

Before we dive into the fixes, let’s quickly review the fundamental principles of a two-stroke engine, like the one in your Stihl 025. A chainsaw engine needs three things to run:

Compression: The piston moving up and down within the cylinder creates pressure, compressing the fuel-air mixture.
Fuel: A properly mixed fuel and oil mixture is crucial for combustion and lubrication.
Spark: The spark plug ignites the compressed fuel-air mixture, causing the explosion that drives the piston.

When the engine is hard to pull with the spark plug installed, it usually points to a compression issue, either too much or something hindering the piston’s movement.

Key Terms Explained

Two-Stroke Engine: An engine that completes a power cycle with two strokes of the piston (up and down) instead of four.
Compression Ratio: The ratio of the volume of the cylinder when the piston is at the bottom of its stroke to the volume when the piston is at the top of its stroke.
Piston: A cylindrical component that moves up and down within the cylinder, driven by the force of combustion.
Cylinder: The chamber in which the piston moves.
Spark Plug: An electrical device that delivers a high-voltage spark to ignite the fuel-air mixture.
Carburetor: A device that mixes air and fuel in the proper proportions for combustion.
Decompression Valve: A valve that, when opened, releases some of the compression in the cylinder, making the engine easier to pull over. Some chainsaws have this, the Stihl 025 does not.
Green Wood: Freshly cut wood with a high moisture content (often above 50%).
Seasoned Wood: Wood that has been dried to reduce its moisture content (typically below 20%). Seasoned wood is easier to burn and produces more heat.

The 3 Fixes for a Hard-to-Pull Stihl 025

Here are three common causes and their solutions for a Stihl 025 that is hard to pull when the spark plug is installed:

1. Excessive Fuel in the Cylinder (Flooding)

The Problem:

One of the most common reasons for a hard-to-pull chainsaw is a flooded engine. This happens when too much fuel enters the cylinder, making it difficult for the piston to compress the mixture. The excess fuel creates a hydraulic lock. Think of it like trying to compress water – it’s much harder than compressing air.

My Experience:

I once spent an entire afternoon wrestling with a Stihl 025 that wouldn’t start. I kept pulling and pulling, convinced it was a spark issue. Finally, in desperation, I removed the spark plug, and a stream of fuel shot out. It turns out, I had over-primed the engine, and the cylinder was flooded.

Step-by-Step Solution:

Safety First: Disconnect the spark plug wire from the spark plug to prevent accidental starting.
Remove the Spark Plug: Use a spark plug wrench (typically 19mm or 3/4 inch) to carefully remove the spark plug.
Inspect the Spark Plug: Examine the spark plug. If it’s wet with fuel, it’s a clear sign of flooding. Clean the spark plug with a wire brush or replace it if it’s fouled. A fouled spark plug is one that’s coated in carbon or oil, preventing it from sparking properly.
Clear the Cylinder: With the spark plug removed, turn the chainsaw upside down. Pull the starter cord several times (5-10 times) to expel the excess fuel from the cylinder. You may see fuel dripping out of the spark plug hole.
Dry the Spark Plug: If you’re reusing the spark plug, dry it thoroughly with a clean cloth or paper towel.
Reinstall the Spark Plug: Carefully thread the spark plug back into the cylinder head by hand to avoid cross-threading. Once it’s snug, tighten it with the spark plug wrench. Don’t overtighten it, as this can damage the cylinder head. A good rule of thumb is to tighten it about 1/4 turn past snug.
Reconnect the Spark Plug Wire: Reattach the spark plug wire to the spark plug.
Start the Chainsaw: Now, try starting the chainsaw. It may take a few pulls to get it going, but it should be significantly easier than before. Avoid using the choke initially, as this can introduce more fuel into the cylinder.

Why This Works:

Removing the spark plug and pulling the starter cord allows you to physically expel the excess fuel from the cylinder, restoring the proper air-fuel ratio.

Pro Tip:

To prevent flooding in the future, avoid over-priming the chainsaw. Typically, 3-5 pumps of the primer bulb are sufficient. Also, ensure that the choke is properly engaged and disengaged during the starting process.

2. Binding or Obstruction in the Engine

The Problem:

Sometimes, the hard-to-pull issue isn’t related to fuel at all. It could be caused by a mechanical obstruction or binding within the engine itself. This could be due to:

Debris in the Cylinder: Small pieces of dirt, sawdust, or carbon buildup can get into the cylinder and interfere with the piston’s movement.
Piston Ring Issues: The piston rings, which seal the gap between the piston and the cylinder wall, can become worn, broken, or stuck, causing increased friction.
Crankshaft or Connecting Rod Problems: While less common, damage to the crankshaft or connecting rod can also cause binding.
Incorrect Assembly: If you’ve recently worked on the chainsaw, an incorrect assembly can cause parts to bind.

My Experience:

I once bought a used Stihl 025 that was advertised as “needing a little TLC.” When I tried to start it, the pull cord was incredibly stiff. After some investigation, I discovered that a small piece of carbon had broken off inside the cylinder and was jamming the piston.

Step-by-Step Solution:

Important Note: This fix involves disassembling parts of the chainsaw engine. If you’re not comfortable with this, it’s best to take it to a qualified repair technician.

Safety First: Disconnect the spark plug wire from the spark plug.
Remove the Muffler: The muffler is usually held in place by a few screws. Removing it will give you a better view of the piston.
Inspect the Piston: Shine a flashlight into the exhaust port and try to get a glimpse of the piston. Look for any signs of scoring (scratches) or damage.
Remove the Cylinder Head (if necessary): If you suspect debris in the cylinder or piston ring issues, you may need to remove the cylinder head. This typically involves removing several bolts. Important: Before removing the cylinder head, mark its orientation so you can reinstall it correctly.
Inspect the Cylinder and Piston: Once the cylinder head is removed, carefully inspect the cylinder walls and the piston for any signs of damage, scoring, or debris.
Clean the Cylinder and Piston: If you find debris, carefully remove it with a soft cloth or brush. Be careful not to scratch the cylinder walls.
Check the Piston Rings: Examine the piston rings for wear, damage, or if they are stuck in their grooves. If they are stuck, you can try to gently free them with a small pick or screwdriver. If they are worn or damaged, they should be replaced.
Reassemble the Engine: Carefully reassemble the engine, ensuring that all parts are properly aligned and tightened to the manufacturer’s specifications. If you removed the cylinder head, use a new head gasket.
Test the Engine: Reconnect the spark plug wire and try starting the chainsaw. If the binding is resolved, the engine should be much easier to pull over.

Why This Works:

By disassembling and inspecting the engine, you can identify and remove any obstructions or binding issues that are preventing the piston from moving freely.

Pro Tip:

When reassembling the engine, use a small amount of two-stroke oil to lubricate the piston and cylinder walls. This will help to reduce friction and ensure smooth operation.

Case Study:

I once worked on a Stihl 025 that had been stored for a long time. When I tried to start it, the pull cord was almost impossible to move. After removing the cylinder head, I discovered that the piston rings were completely stuck in their grooves due to dried-up oil. I carefully freed the rings, cleaned the cylinder and piston, and reassembled the engine. The chainsaw started on the second pull!

3. Excessive Compression

The Problem:

While seemingly counterintuitive, excessive compression can also make a chainsaw hard to pull. This is more common in older engines or engines that have been modified. High compression can be beneficial for power output, but it also requires more force to overcome when starting the engine. While the Stihl 025 is not known for excessive compression, it is worth exploring.

Why would compression be too high?

Carbon Buildup: Excessive carbon buildup in the combustion chamber can reduce the volume of the chamber, effectively increasing the compression ratio.
Incorrect Head Gasket: If the head gasket is too thin, it can also increase the compression ratio. (This is less likely unless the head gasket has been replaced)

My Experience:

I once worked on a modified chainsaw that had a very high compression ratio. It was a beast when it was running, but it was incredibly difficult to start. The owner had to use a special technique to get it going.

Step-by-Step Solution:

Consider a Decompression Valve (Not applicable to Stihl 025): Some chainsaws have a decompression valve that can be opened to release some of the compression when starting. The Stihl 025 does not have one.
Check for Carbon Buildup: Remove the spark plug and use a small inspection camera or a bent wire to check for excessive carbon buildup on the piston and cylinder head. If you find a significant amount of carbon, you will need to remove the cylinder head and clean it.
Clean Carbon Deposits: Carefully scrape away carbon deposits using a plastic scraper or a specialized carbon cleaning tool. Avoid using metal tools that could damage the cylinder head or piston.
Inspect the Head Gasket: If you removed the cylinder head, inspect the head gasket for damage or incorrect thickness. Replace it if necessary.
Reassemble and Test: Reassemble the engine and test the compression. If the compression is still too high, you may need to consider other modifications, such as installing a thicker head gasket or modifying the piston.

Why This Works:

Removing carbon buildup increases the combustion chamber volume, reducing the compression ratio and making the engine easier to pull over.

Pro Tip:

Regularly cleaning the cylinder head and piston can help prevent excessive carbon buildup and maintain optimal engine performance.

Additional Tips and Considerations

Fuel Mixture: Ensure that you’re using the correct fuel-to-oil ratio for your Stihl 025. Typically, this is 50:1 (50 parts gasoline to 1 part two-stroke oil). Using the wrong mixture can lead to engine problems.
Fuel Quality: Use fresh, high-quality gasoline. Old or stale gasoline can be difficult to ignite.
Air Filter: A dirty air filter can restrict airflow to the carburetor, causing the engine to run rich and become difficult to start. Clean or replace the air filter regularly.
Carburetor Adjustment: In some cases, a hard-to-pull chainsaw can be caused by an improperly adjusted carburetor. If you’re comfortable adjusting the carburetor, consult your owner’s manual for the proper settings. However, if you’re not familiar with carburetor adjustment, it’s best to take it to a qualified technician.
Starter Mechanism: Inspect the starter mechanism (the pull cord and recoil spring) for any signs of damage or wear. A worn or damaged starter mechanism can make it difficult to pull the cord.
Check Flywheel Key: The flywheel key is a small part that aligns the flywheel with the crankshaft. If the flywheel key is sheared or damaged, it can cause timing issues and make the engine difficult to start.
Check for Spark: Even if the spark plug is new, check to make sure it’s producing a strong spark. Use a spark tester or hold the spark plug against the engine block (while wearing insulated gloves) and pull the starter cord. You should see a bright blue spark. A weak or nonexistent spark can indicate a problem with the ignition system.
When to Seek Professional Help: If you’ve tried all of these fixes and your chainsaw is still hard to pull, it’s time to take it to a qualified repair technician. There may be a more serious underlying problem that requires professional attention.

Safety Precautions

Always disconnect the spark plug wire before working on the chainsaw. This will prevent accidental starting.
Wear safety glasses and gloves when working on the chainsaw.
Work in a well-ventilated area.
Be careful when handling gasoline. Gasoline is highly flammable.
If you’re not comfortable with any of these repairs, take the chainsaw to a qualified repair technician.

Chainsaw Maintenance for Easier Starting

Preventative maintenance is key to avoiding starting problems in the first place. Here are some routine tasks:

Regularly clean or replace the air filter. A clean air filter ensures proper airflow to the carburetor.
Use fresh fuel and the correct fuel-to-oil ratio.
Inspect and clean the spark plug regularly.
Keep the chain sharp. A sharp chain reduces the load on the engine and makes it easier to start.
Store the chainsaw properly. When storing the chainsaw for an extended period, drain the fuel tank and run the engine until it stalls to prevent fuel from gumming up the carburetor.
Sharpening Chainsaws: Use a chainsaw file to sharpen the cutters. Maintain the correct angle and depth for optimal cutting performance. A dull chain requires more force from the engine.

Wood Processing and Firewood Preparation: A Quick Overview

Since we’re talking chainsaws, it’s worth touching on wood processing and firewood preparation.

Felling Trees: Use proper felling techniques to ensure the tree falls in a safe direction. This includes making a notch cut and a back cut.
Debarking Logs: Removing the bark can speed up the drying process and reduce the risk of insect infestation.
Splitting Firewood: Use a maul, axe, or log splitter to split the logs into manageable pieces. A hydraulic log splitter significantly increases efficiency for large volumes.
Stacking Firewood: Stack the firewood in a way that allows for good airflow to promote drying.
Drying Firewood: Seasoned wood burns more efficiently and produces more heat. Allow the firewood to dry for at least six months, or preferably a year, before burning it. Target moisture content is below 20%.
Wood Types: Hardwoods like oak, maple, and ash are ideal for firewood because they burn longer and produce more heat than softwoods like pine and fir.
Firewood Stacking Techniques: Consider using a “Holz Hausen” stack, a circular method that promotes good airflow and shedding of rain.

Case Study: Firewood Production

A small-scale logging operation aims to produce 50 cords of firewood annually. The process includes:

Felling: Using Stihl MS 271 and Stihl MS 462 chainsaws for felling trees.
Bucking: Cutting felled trees into manageable lengths (16-18 inches) using the same chainsaws.
Splitting: Using a 25-ton hydraulic log splitter to split the logs.
Stacking: Stacking the firewood in rows, allowing for air circulation.
Drying: Allowing the firewood to dry for 12 months before selling it.
Measurements: Each cord measures 4 ft x 4 ft x 8 ft.

Benefits of Hydraulic Splitter:

Increased efficiency compared to manual splitting.
Reduced physical strain on workers.
Ability to split larger and tougher logs.

Final Thoughts

A hard-to-pull chainsaw can be a frustrating problem, but by understanding the potential causes and following these step-by-step fixes, you can often resolve the issue yourself. Remember to always prioritize safety and seek professional help when needed. With proper maintenance and care, your Stihl 025 (or any chainsaw) will provide you with years of reliable service.

Chainsaw Hard to Pull with Spark Plug In (3 Fixes for Stihl 025)