Honda UMK425T Owner's Manual page 16

To ensure safe operation
Carbon Monoxide Poisoning Hazard
Exhaust contains poisonous carbon monoxide, a colorless and odorless
gas. Breathing exhaust can cause loss of consciousness and may lead
to death.
• If you run the engine in an area that is confined or even partially
enclosed, the air you breathe could contain a dangerous amount of
exhaust gas. To keep exhaust gas from building up, provide adequate
ventilation.
• Replace faulty muffler.
• Do not operate the engine in a confined space where dangerous
carbon monoxide fumes can collect.
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