A chainsaw that refuses to start is more than inconvenient—it can derail an entire day’s work. Whether you’re clearing storm damage or doing routine tree maintenance, a non-starting chainsaw is frustrating. The good news: two-stroke chainsaw engines are relatively simple, and most starting problems trace back to a few common causes. Systematic troubleshooting identifies the problem faster than random part replacement.

Two-Stroke Engine Basics
Fuel System Problems
Ignition Issues
Air and Compression
Starting Procedure Review
Troubleshooting Quick Reference
Frequently Asked Questions

Two-Stroke Engine Basics

Understanding two-stroke operation helps diagnose problems effectively. These engines are simpler than four-strokes but have specific requirements.

Chainsaw ready for troubleshooting Two-stroke engines require proper fuel mix and correct starting procedure

Two-stroke engines require oil mixed directly with fuel since they lack a separate oil reservoir like four-stroke engines. The oil in the fuel lubricates internal components as it passes through. Using straight gasoline destroys the engine quickly—often within minutes. Using incorrect mix ratios causes problems ranging from smoking to seizure.

Standard mix ratios:

Most modern chainsaws: 50:1 (2.6 oz oil per gallon gas)
Older chainsaws: 40:1 or 32:1
Always check manufacturer specifications

Why fuel mix matters:

Too little oil = insufficient lubrication, engine damage
Too much oil = carbon buildup, fouled plug, poor running
Wrong oil type = inadequate protection at high RPM

Fuel System Problems

Fuel issues cause most chainsaw starting failures, especially after storage.

Old or Bad Fuel

Two-stroke fuel mix degrades faster than straight gasoline. After 30 days, performance suffers. After 90 days, starting becomes difficult.

Solution:

Drain old fuel completely
Mix fresh fuel with quality two-stroke oil
Use fuel stabilizer for any fuel that may sit

Flooded Engine

Over-priming or excessive choke use floods the engine with fuel.

Symptoms:

Strong fuel smell
Wet spark plug
Engine cranks but won’t fire

Solution:

Set choke to OFF/RUN position
Hold throttle wide open
Pull starter 10-15 times to clear excess fuel
Return throttle to normal and try starting

Clogged Fuel Filter

The fuel filter sits inside the tank, attached to the fuel line.

Symptoms:

Engine starts then dies
Won’t rev under load
Fuel starvation symptoms

Solution: Pull fuel line from tank, replace filter attached to end.

Carburetor Issues

Varnish from old fuel clogs tiny carburetor passages.

Symptoms:

No fuel reaching engine
Engine won’t idle properly
Poor performance when running

Solution: Clean or rebuild carburetor. Chainsaw carburetors are small and delicate—consider professional service if unfamiliar.

Chainsaw carburetor Carburetor cleaning often resolves starting issues

Ignition Issues

Without spark, fuel won’t ignite regardless of how good the fuel system is.

Spark Plug Problems

Spark plugs foul, wear and fail.

Testing:

Remove spark plug
Connect to plug wire
Ground electrode against cylinder
Pull starter and observe spark

Good spark: Bright blue, consistent Bad spark: Weak, yellow, intermittent, or none

Solution: Replace spark plug. Use correct heat range and gap (typically 0.020-0.025”).

Ignition Coil Failure

The ignition coil generates spark voltage. Heat and age cause failure.

Symptoms:

No spark with new plug
Engine dies when hot, restarts when cool
Intermittent spark

Solution: Replace ignition coil. Usually 2 screws and 1-2 wire connections.

Kill Switch Problems

A shorted or stuck kill switch grounds ignition, preventing spark.

Test: Disconnect kill switch wire. If engine starts, repair or replace switch.

Air and Compression

Dirty Air Filter

Clogged filters restrict airflow, causing rich running and hard starting.

Solution: Clean or replace air filter. Chainsaw filters get dirty quickly in sawdust environments—check frequently.

Compression Loss

Worn piston rings or cylinder, scored cylinder walls, or gasket leaks cause compression loss.

Symptoms:

Pull cord feels easier than normal
Engine won’t fire despite good fuel and spark
Compression test shows low readings

Solution: Professional repair needed for internal engine problems.

Air filter inspection Check air filter condition regularly

Starting Procedure Review

Improper starting technique causes many “won’t start” situations.

Cold Start Procedure

Set chain brake
Place saw on ground, secure with foot in handle
Set choke to FULL/CLOSED
If equipped, prime bulb 5-6 times
Pull starter until engine fires (usually 3-5 pulls)
Move choke to HALF
Pull until engine runs
Move choke to OFF/RUN
Blip throttle to clear

Warm Start Procedure

Choke OFF
Pull starter—should start in 1-2 pulls

Common Mistakes

Over-choking warm engine
Not using enough choke on cold engine
Insufficient priming
Not securing saw during starting

Troubleshooting Quick Reference

Symptom	Likely Cause	Solution
Won’t start, no spark	Bad plug or coil	Test spark, replace plug
Won’t start, has spark	Fuel issue	Check fuel, clean carb
Starts, dies immediately	Choke stuck, air leak	Check choke, inspect gaskets
Starts, dies under load	Fuel filter clogged	Replace fuel filter
Hard to start cold	Normal or weak spark	Check procedure, replace plug
Hard to start hot	Vapor lock or coil	Wait to cool, test coil
Only runs on choke	Lean condition	Clean carb, check air leaks
Floods easily	Over-priming	Reduce priming, check carb
Pull cord feels loose	Low compression	Test compression

Frequently Asked Questions

Why won’t my chainsaw start after sitting all winter?

Old fuel is almost always the cause. Two-stroke fuel mix degrades quickly, and after a few months, varnish forms in the carburetor. Drain old fuel completely, add fresh 50:1 mix with stabilizer, and try starting. If it still won’t start, the carburetor likely needs cleaning to remove varnish deposits from the tiny passages.

How do I know if my chainsaw is flooded?

Strong fuel smell at the spark plug area and a wet or fuel-soaked spark plug indicate flooding. This happens from over-priming or excessive choke use. Clear flooding by removing the spark plug, setting choke to OFF, holding throttle wide open, and pulling the starter 10-15 times. Reinstall a dry plug and start without choke.

What causes a chainsaw to start then die?

Usually fuel delivery problems. The engine fires on fuel in the carburetor bowl but can’t sustain running because fuel isn’t flowing properly. Check the fuel filter first (inside the tank, attached to fuel line), then inspect fuel lines for cracks or collapse. If those are good, the carburetor likely needs cleaning or the diaphragm needs replacement.

How often should I change chainsaw spark plugs?

Replace annually or every 100 hours of use, whichever comes first. Spark plugs are inexpensive ($3-8) and are cheap insurance for reliable starting. If you’re having starting issues and can’t remember when you last changed the plug, start there.

Can I use regular gas in a chainsaw?

Never use straight gasoline in a two-stroke chainsaw—it will destroy the engine within minutes. Two-strokes require oil mixed with fuel for lubrication. Always use properly mixed two-stroke fuel at the ratio specified by your chainsaw manufacturer (usually 50:1).

Why does my chainsaw only run on choke?

The engine is running too lean on normal settings. With choke on, the fuel mixture is artificially enriched, compensating for the problem. Common causes include clogged carburetor jets, air leaks at intake gaskets or crankshaft seals, or incorrect carburetor adjustment. Clean the carburetor first, then check for air leaks.

What’s the best fuel for chainsaws?

Fresh 87+ octane gasoline mixed with quality synthetic two-stroke oil at 50:1 ratio. Use fuel under 30 days old. For fuel that may sit longer, add fuel stabilizer. Pre-mixed fuel (like TruFuel or VP Racing) is more expensive but eliminates mixing errors and storage issues.

Chainsaw spark plug check Check spark plug condition - a wet plug indicates flooding, black deposits indicate rich running

A chainsaw that won’t start usually has a simple fix. Work through fuel, spark and air systematically. Most problems trace back to old fuel or a dirty carburetor. Keep fresh fuel in your saw and it’ll start reliably when you need it.

Chainsaw Won't Start | Troubleshooting Guide

Table of Contents

Two-Stroke Engine Basics