Short answer: When a chainsaw bogs down under load or when you pull the trigger, it's most commonly an air or a fuel problem. A blocked air filter stops the saw reaching full RPM, so it bogs down when you cut into wood. Pop the filter off, knock it out and put it back. If that doesn't fix it, a fuel, carburetor or air-leak problem is a job for your dealer or saw shop.
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What Phil says
"Most commonly it would be an air or a fuel issue. If your air filter's blocked, it's not going to get enough air, so it's not going to run out to its full potential, and when you cut into wood, it's going to bog down. You'll notice it too if you're not cutting and you just run the saw out, it's not going to reach its full RPM, so you can listen, and if you're familiar with your saw, you'll know that it's not running out to the full RPMs."
"Alternatively, it could be that it's not getting enough fuel, maybe you've got a carburettor issue, or it could be that you have an air leak somewhere. That's a bad day. That's a definitely take it to the shop, unless you're a hardcore DIYer and you want to replace crank seals, but I wouldn't recommend that without the right tools."
How to tell
Run the saw out without cutting and listen. If you know your saw, you'll hear it if it isn't reaching its full RPM.
The checklist
- Air filter first. It's the easy one. Pop it off, knock it out, put it back in.
- Listen again. Run the saw out. Is it reaching full revs now?
- Fuel. Not getting enough fuel can cause the same symptom. It might be the carburetor, or it might just need a tune.
- Air leak. Phil calls this the bad day. Fixing it can mean replacing crank seals, which he wouldn't recommend without the right tools.
When to take it to the shop
If a clean air filter doesn't fix it, it's likely fuel, the carburetor or an air leak. "Could be just a tune. You'll find out if you take it to your dealer or your local chainsaw shop."
Free one-page checklist
Phil’s chainsaw troubleshooting checklist
Seven common problems, the checks a working arborist runs first, and when it’s a job for the saw shop. Print it and keep it with your saw.
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From Clogger Answers, episode 1. These are Phil's opinions, based on his professional experience. Always follow your saw's manual and wear the right protective gear.
Phil is a professional arborist based in Invercargill, New Zealand, who runs saws every day with his crew. Clogger makes chainsaw pants and chainsaw chaps.