Chainsaw Won't Start? Check These 6 Things First
A chainsaw that won’t start is usually caused by old fuel (90% of cases), a flooded engine or a fouled spark plug. Fix old fuel issues by draining the tank and adding fresh 50:1 mix—two-stroke fuel goes bad in 30-90 days. Clear a flooded engine by removing the spark plug, pulling the cord 10-15 times with choke off, then reinstalling the dry plug. Carburetor cleaning costs $30-50 DIY or $75-150 at a shop if fresh fuel doesn’t solve it.
Chainsaw starting problems almost always come down to fuel or spark. Two-stroke engines are simple machines—once you understand how they work, troubleshooting gets straightforward. Below, certified mechanic Tom Bradley covers the most common reasons chainsaws won’t start and explains how to fix each one.
Engine Basics
Chainsaws use two-stroke engines, which work differently than the four-stroke engines in your car or lawn mower. Knowing these differences lets you diagnose problems.
Two-strokes need oil in the fuel. There’s no separate oil reservoir—the engine gets lubrication from oil mixed directly with the gasoline. Run straight gas in a two-stroke and you’ll destroy the engine in minutes. Most modern chainsaws use a 50:1 mix ratio (2.6 ounces of two-stroke oil per gallon of gas). Older saws might require 40:1 or 32:1.
Two-stroke fuel goes bad faster. The oil-gas mixture degrades quicker than straight gasoline. After 30 days, you’ll notice performance issues. After 90 days, the saw probably won’t start at all. That fuel you mixed last fall isn’t going to work this spring.
Two-strokes are sensitive to fuel quality. The tiny passages in a chainsaw carburetor clog easily. Bad fuel, wrong mix ratios, or fuel that’s been sitting too long all cause problems.
Starting Mistakes to Avoid
Don’t keep pulling the cord. If it hasn’t started after 10 to 15 pulls, stop. You’re either flooding the engine or there’s a problem that more pulling won’t fix. Step back and troubleshoot.
Don’t use old fuel. If the saw has been sitting for more than a month or two, drain the fuel and start fresh. Old fuel is the number one cause of chainsaw starting problems.
Don’t skip the proper starting procedure. Two-strokes have a specific starting sequence with choke positions and priming. Doing it wrong floods the engine or leaves it fuel-starved.
Don’t use straight gasoline. This destroys two-stroke engines. If you’re not sure what’s in the tank, dump it and mix fresh fuel properly.
Old Fuel Problems
If your chainsaw sat over winter with fuel in it, you’ve probably found your problem. Two-stroke fuel mix degrades in 30 to 90 days. The lighter compounds evaporate, leaving behind a gummy varnish that coats the inside of the carburetor and blocks the tiny jets and passages.
How to Fix It
- Drain all the old fuel from the tank
- Press the primer bulb repeatedly to push old fuel out of the carburetor and lines
- Mix fresh fuel using the correct ratio (usually 50:1) with quality two-stroke oil
- Fill the tank and try starting
If fresh fuel gets the saw running, you got lucky. Add fuel stabilizer to any mix that might sit for more than a few weeks. If fresh fuel doesn’t help, the carburetor is probably clogged with varnish and needs cleaning. Many chainsaws use Zama carburetors or Walbro WYL carburetors.
Flooded Engine Fix
Flooding happens when too much fuel enters the cylinder and there’s not enough air for combustion. The spark plug gets soaked and can’t ignite the mixture.
Signs of Flooding
- Strong gasoline smell near the engine
- Wet spark plug when you pull it out
- Engine turns over freely but won’t fire
- You’ve been pulling the cord a lot with the choke on
How to Clear a Flooded Chainsaw
- Set the choke to OFF or RUN position
- Set the throttle to wide open (full trigger squeeze)
- Pull the starter cord 10 to 15 times—this pushes excess fuel out
- Remove the spark plug and check if it’s wet
- If wet, wipe it dry with a clean rag or replace it
- Reinstall the plug and try starting with NO choke and NO priming
The engine should fire within a few pulls. If it sputters and wants to die, it’s still clearing excess fuel. Let it run.
What Causes Flooding
- Too many primer bulb pushes (5 to 6 is enough for a cold start)
- Leaving the choke on too long after the engine fires
- Repeated starting attempts without letting the engine clear
- Trying to start a warm saw with the choke on
No Spark Diagnosis
No spark means no combustion, no matter how good your fuel is. Here’s how to test.
The Spark Test
- Remove the spark plug using the correct socket (usually 13/16” or 3/4”)
- Reconnect the spark plug wire to the plug
- Hold the plug threads against a bare metal surface on the engine (ground it)
- Pull the starter cord and watch the electrode gap
What you want: A bright blue spark jumping across the gap with each pull. Use a circuit tester or voltage tester if you want to measure the output.
What’s wrong: No spark, weak orange/yellow spark, or intermittent spark.
If There’s No Spark
Replace the spark plug first. It’s cheap ($4 to $8) and often fixes the problem. Chainsaw plugs foul from two-stroke oil and should be replaced annually anyway.
Check the kill switch. A stuck or shorted kill switch grounds the ignition and prevents spark. Disconnect the kill switch wire from the ignition module and test again. If you get spark now, the switch is bad.
Test the ignition coil. If a new plug doesn’t help and the kill switch isn’t the problem, the ignition coil has probably failed. Coils fail from heat and age. Replacement coils run $15 to $40 depending on the saw.
Fuel Delivery Problems
If you have spark and fresh fuel but the saw still won’t start, fuel isn’t reaching the engine properly.
Clogged Fuel Filter
The fuel filter lives inside the gas tank, attached to the end of the fuel line. Over time it clogs with debris and restricts fuel flow.
Symptoms:
- Engine starts but dies when you give it throttle
- Saw runs for a few seconds then quits
- Won’t rev up under load
The fix: Pull the fuel line out of the tank (a piece of wire with a hook works well) and replace the filter attached to the end. Fuel filters cost $3 to $8.
Cracked or Collapsed Fuel Lines
The rubber fuel lines inside the tank can crack, harden, or collapse over time. Cracked lines let air into the system. Collapsed lines restrict fuel flow.
Check: Pull the fuel line out of the tank and inspect it. Squeeze it—it should be pliable, not stiff. Look for cracks, especially near the tank grommet.
The fix: Replace the fuel lines. A complete fuel line kit for most saws runs $10 to $20.
Chainsaw Carburetor Problems
If the fuel filter and lines are good but the saw still won’t run right, the carburetor needs attention. Old fuel leaves varnish deposits that clog the tiny jets and passages inside.
Signs of carburetor problems:
- Engine won’t idle
- Only runs with choke on (running lean)
- Bogs down when you give it throttle
- Won’t start at all despite good spark and fresh fuel
The fix: Clean or rebuild the carburetor. Chainsaw carburetors are small and delicate. If you’re comfortable with small engine work, a rebuild kit costs $10 to $20 and includes new gaskets and diaphragms. If you’re not comfortable, a shop will clean it for $50 to $75.
Correct Starting Procedure
Many “won’t start” problems are actually operator error. Two-stroke engines need a specific starting sequence.
Cold Start (Engine hasn’t run recently)
- Set the chain brake for safety
- Place the saw on the ground with your foot through the rear handle to secure it
- Set the choke to FULL or CLOSED position
- Push the primer bulb 5 to 6 times until you see fuel in the bulb
- Pull the starter cord until the engine fires or “pops” (usually 3 to 5 pulls)
- Move the choke to HALF position
- Pull until the engine starts and runs
- Immediately move choke to OFF/RUN position
- Blip the throttle to clear any remaining rich mixture
Warm Start (Engine ran in the last few minutes)
- Choke stays OFF
- No priming needed
- Pull the starter—should fire in 1 to 2 pulls
Hot Start (Engine is hot, been running hard)
Same as warm start. Don’t use choke on a hot engine—you’ll flood it.
Compression Problems
If fuel and spark check out but the saw still won’t start, you might have a compression issue. This is less common but possible on older or heavily used saws.
Signs of Low Compression
- Pull cord feels easier than normal—less resistance
- Engine turns over very easily
- Won’t fire despite confirmed fuel and spark
What Causes Compression Loss
- Worn piston rings
- Scored cylinder walls
- Blown head gasket or base gasket
- Damaged crankshaft seals
Compression problems require internal engine work. For most homeowner saws, it’s often more cost-effective to replace the saw than rebuild the engine. Professional-grade saws might be worth repairing.
Quick Reference
| Problem | Likely Cause | Fix |
|---|---|---|
| Won’t start, no spark | Bad plug or coil | Replace plug, test coil |
| Won’t start, has spark | Fuel issue | Fresh fuel, check filter and carb |
| Starts then dies immediately | Clogged fuel filter | Replace filter |
| Only runs on choke | Running lean, carb issue | Clean carburetor, check for air leaks |
| Floods easily | Over-priming, stuck needle valve | Adjust technique, clean carb |
| Hard to pull, won’t fire | Low compression | Test compression, likely major repair |
Tools and Parts Needed
Tools:
- Spark plug socket (13/16” or 3/4”)
- Screwdriver set
- Wire hook for pulling fuel line from tank
- Compressed air (for carburetor cleaning)
Materials:
- Fresh gasoline (87+ octane)
- Quality two-stroke oil
- Fuel stabilizer
- Replacement spark plug ($4 to $8)
- Fuel filter ($3 to $8)
- Carburetor rebuild kit ($10 to $20, if needed)
Prevention Tips
Use Fuel Stabilizer
Add stabilizer to every batch of two-stroke mix. It extends fuel life from 30 days to 6 to 12 months.
Run the Tank Dry for Storage
Before putting the saw away for the season, run it until it dies from fuel starvation. This prevents fuel from sitting in the carburetor and leaving varnish deposits. See our small engine storage guide for the full process.
Replace the Spark Plug Annually
Even if the saw starts fine, a fresh plug ensures reliable starting. It’s cheap insurance.
Keep the Air Filter Clean
Chainsaw air filters clog quickly in dusty, sawdust-heavy environments. Check and clean or replace the filter regularly—every few tanks of fuel if you’re cutting a lot.
Summary
A chainsaw that won’t start is usually a fuel problem. Old gas, a flooded engine, or a clogged carburetor account for most failures. Start by draining old fuel and filling with fresh 50:1 mix. If that doesn’t work, check for spark and test the fuel delivery system.
The key is working through the possibilities systematically rather than randomly replacing parts. Most chainsaw starting problems cost under $20 to fix yourself once you identify the cause.