Short answer: There are three likely causes. Too much two-stroke oil in your fuel. No oil in your fuel at all, which can destroy the saw. Or depth gauges (rakers) filed too low, so the saw keeps stalling in the cut and burns the clutch out. Check your fuel mix before anything else.
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What Phil says
"You could have too much oil in your fuel, too much two-stroke oil in your fuel, so just make sure the mix is correct before you go and put it in your saw. Another reason is you could have put no oil in your fuel, and that'd be a really bad day because that means your saw is toast. So don't do that. Another reason might be that you've set your rakers or depth gauges too low, and you keep stalling the saw, and you're burning your clutch out, and that'll also smoke."

The three causes
| Cause | What's happening | What to do |
|---|---|---|
| Too much two-stroke oil | The fuel mix is too rich in oil | Mix to your saw's specified ratio before you fill up |
| No oil in the fuel | The engine is running without lubrication | Stop. Phil: "That means your saw is toast." |
| Rakers filed too low | The saw keeps stalling in the cut and burns the clutch | Reset your depth gauges to the correct depth |

Get the mix right
Your saw's manual gives the fuel mix. Phil's crew runs 50 to 1: 100 ml of two-stroke oil in 5 litres of fuel. Not confident mixing it? Buy premix. More on fuel mix and premix.

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.