Chainsaw won't start when hot: flooded, spark plug, or compression?

"It starts perfectly in the morning, but impossible to restart after a break." This specific symptom—refusal to start when hot—has well-identified causes on a 2-stroke engine. As always, we go from free fixes to more serious ones.

1. Hot-start technique

First instinct, often the right one: when hot, do NOT start with the choke closed. Closing the choke on an already warm engine floods it immediately. When hot, choke open, light throttle, one or two pulls are enough. Many "breakdowns" when hot are just this.

2. A flooded engine

If you've pulled the starter several times with the choke closed, the chainsaw is probably flooded (wet spark plug, smell of fuel). Solution: choke open, full throttle, and pull several times to purge the excess. On certain models, you remove the spark plug to dry it.

3. The spark plug

A fouled spark plug or incorrect gap passes when cold but fails when hot. It's a quick check: color, gap, electrode condition. A black and wet spark plug indicates too-rich mixture or overly generous 2-stroke oil ratio.

4. Fuel and mixture

E10 gasoline stored too long or a poorly mixed 2-stroke ratio disturbs starting, especially when hot. Make a fresh mixture at the correct ratio with recent fuel before going further. A clogged fuel filter and air filter also play a role: see complete chainsaw maintenance.

5. The serious culprit: air leak and compression

If everything else checks out, the classic problem on an aging 2-stroke is air leak at the crankshaft seal (spi) or crankcase. When the engine is hot, hardened seals let air in, the mixture leans out, and hot starting becomes impossible. Weak compression (worn piston ring) gives the same symptom. Here we enter the domain of pressure/vacuum pump inspection.

For a specific model, the Stihl MS 261 technical sheet gathers settings and weak points. Regular maintenance (filter, spark plug, fresh fuel mix) prevents most hot-start refusals.

Describe the exact behavior to the mechanic AI (starts cold, refuses hot, spark plug wet or dry): it separates simple starting technique from real mechanical failure.