Honda 2005 VTX1800C Owner's Manual page 221

Catalytic Converter
Both Types of Catalytic Converters:
Catalytic converters must operate at a high
temperature for the chemical reactions to
take place. They can set fire to any
combustible materials that come near them.
Park your motorcycle away from high
grasses, dry leaves, or other flammables.
212
Technical Information
A defective catalytic converter contributes
to air pollution, and can impair your
engine's performance. Follow these
guidelines to protect your motorcycle's
catalytic converter.
Always use unleaded gasoline. Even a
small amount of leaded gasoline can
contaminate the catalyst metals, making
the catalytic converter ineffective.
Keep the engine tuned-up.
Have your motorcycle diagnosed and
repaired if it is misfiring, backfiring,
stalling or otherwise not running
properly.