Intro
Hey, welcome back to Backyard Engine Pro. If your chainsaw won’t start after sitting for weeks or months, you’re in good company. This is one of the most common small engine problems there is, and chainsaws are particularly susceptible because they run on a two-stroke fuel mix that goes bad faster than straight gasoline. Add in a carburetor full of varnish deposits and a corroded spark plug and you’ve got a saw that just won’t cooperate.
The good news? Most of these problems are easy to fix at home without any special tools. Let’s work through them one by one and get your saw running again.
Quick Fix Overview
- Old or bad fuel
- Clogged carburetor
- Dirty spark plug
- Clogged air filter
- Fuel line blockage
- Flooded engine
- Incorrect choke use
Why Your Chainsaw Won’t Start After Sitting
When a chainsaw sits unused, several things happen at once. The fuel mix degrades and leaves behind sticky varnish deposits in the carburetor. The spark plug accumulates moisture and corrosion. Rubber fuel lines harden and crack. Air filters collect dust and debris. Any one of these on its own can prevent starting, and after a long storage period you may be dealing with more than one at the same time. Work through the list in order and you’ll find the culprit.
1. Old or Bad Fuel
This is where to start every single time on a chainsaw that’s been sitting. Two-stroke mixed fuel degrades faster than straight gasoline, and the ethanol content in most pump gas accelerates that breakdown significantly. Fuel sitting in the tank for more than 30 days has already started to go stale, and anything older than 60 to 90 days has almost certainly left varnish deposits behind in the fuel system.
What to do:
- Drain the old fuel from the tank completely. Don’t try to dilute it with fresh gas
- Mix a fresh batch at the correct ratio for your saw, typically 50:1 unless your manufacturer specifies otherwise
- Use fresh gasoline as the base, and ethanol-free fuel if it’s available in your area
- Add a quality fuel stabilizer going forward if the saw will be sitting between uses
2. Clogged Carburetor
Even if you drain the old fuel, the damage from it may already be done. Old mixed gas leaves behind a sticky varnish that coats the inside of the carburetor and clogs the tiny jets and passages fuel needs to flow through. The engine may crank and crank but never fire because fuel simply can’t get through.
What to do:
- Spray carb cleaner generously into the carburetor body, jets, and all visible passages
- Give it several minutes to break down deposits before attempting to start
- Remove and deep clean if a spray-down doesn’t do the job
- For heavy varnish buildup, soak the carburetor bowl and jets overnight in fresh carb cleaner and clear all passages with a thin cleaning needle before reassembling
Follow our carburetor cleaning guide for help
3. Dirty or Faulty Spark Plug
A spark plug that’s been sitting for months is a prime candidate for moisture, corrosion, and carbon fouling on the electrode. It may look fine from the outside but produce a weak or inconsistent spark that isn’t enough to ignite the fuel mixture. Since a new trimmer plug costs just a couple of dollars and swaps in minutes, replacing it early in the diagnostic process is almost always worth doing.
What to do:
- Remove and inspect the spark plug carefully
- Clean light carbon deposits from the electrode with a wire brush
- Check the gap with a feeler gauge and adjust if needed. Most two-stroke chainsaw engines call for a gap between 0.025 and 0.030 inches, but check your manual to confirm
- Replace the plug if there’s heavy fouling, corrosion, a cracked porcelain insulator, or a worn electrode
Learn how to replace it in our spark plug guide
4. Dirty Air Filter
A clogged air filter restricts the airflow the engine needs to mix with fuel for combustion. Chainsaws kick up tremendous amounts of sawdust and debris during use, and a filter that wasn’t cleaned before storage is starting the season already compromised. Without adequate airflow the fuel mixture is too rich to ignite properly.
What to do:
- Remove the air filter and inspect it closely
- Tap it firmly against your hand to knock out loose sawdust and debris
- Wash foam filters gently with warm soapy water, rinse thoroughly, and let dry completely before reinstalling. Never reinstall a wet filter
- For felt or paper style filters, tap clean and replace if heavily soiled or showing any signs of damage
- A filter that looks dark and loaded with debris after a storage period is ready to be replaced
5. Fuel Line or Filter Issues
Rubber fuel lines harden, crack, and deteriorate over time, especially when exposed to ethanol fuel during storage. They can collapse internally in a way that’s not visible from the outside, completely blocking fuel flow without any obvious external sign. The fuel filter inside the tank can also gum up and restrict flow to near zero.
What to do:
- Inspect the fuel lines carefully for cracks, hardening, or any sections that look collapsed or deformed
- Pull one end loose from a fitting and blow gently through the line to check for restriction
- Replace any line that shows visible cracking, stiffness, or that won’t pass air freely
- Pull the fuel filter out of the tank using a bent wire or small hook and replace it if it looks dark, clogged, or deteriorated. Fuel filters on chainsaws are inexpensive and easy to replace
6. Flooded Engine
If you’ve been pulling the starter cord repeatedly without success, especially with the choke closed and after priming multiple times, there’s a good chance the engine is flooded. Excess fuel in the cylinder prevents ignition, and the more you pull the worse the situation gets. The telltale sign is a strong smell of fuel coming from the exhaust area or air filter.
What to do:
- Stop pulling the cord and wait 5 to 10 minutes to let excess fuel evaporate from the cylinder
- Remove the spark plug and pull the cord several times to help clear the cylinder, then reinstall
- Set the choke to the open or run position
- Hold the throttle trigger fully open if your saw has one
- Attempt a normal start once the strong fuel smell has faded
7. Incorrect Choke Use
The choke is one of the most misunderstood controls on a chainsaw, and using it incorrectly is one of the most common reasons a saw won’t start. A cold engine needs the choke closed to create a richer fuel mixture that’s easier to ignite. Once the engine fires, you need to move the choke to the open or half position immediately or it will flood and stall right out.
What to do:
- Set the choke to the CLOSED position before attempting to start a cold engine
- Pull the cord until the engine pops or fires briefly, which is called a false start. This is normal and means you’re close
- After that first pop, move the choke to the half or open position and pull again. The engine should start on the next pull or two
- If the engine is already warm from a recent attempt, start with the choke open or in the half position rather than fully closed
Common Mistakes to Avoid
- Trying to start on old or improperly mixed fuel and wondering why it won’t cooperate
- Over-priming the primer bulb and flooding the engine before the first pull
- Ignoring airflow issues and skipping the air filter inspection after storage
- Leaving the choke closed too long after the engine fires and flooding it back out
Pro Tip
Start with two things every time a chainsaw won’t start after sitting: fresh fuel at the correct mix ratio and a clean or new spark plug. These two fixes resolve the majority of post-storage starting problems and together cost next to nothing. Get those done first before you pull the carburetor or adjust anything else.
Final Thoughts
A chainsaw that won’t start after sitting is almost always a fixable problem. Work through the list from top to bottom, start with the simple stuff, and you’ll have your saw running again without a trip to the shop.
Now go get that wood cut. You’ve got this.