Honda CRF250X 2007 Owner's Manual & Competition Handbook page 164

Emission Control Systems
Source of Emission
The combustion process produces carbon
monoxide (CO), oxides of nitrogen (NOx), and
hydrocarbons (HC).
Control of hydrocarbons and oxides of nitrogen
is very important because, under certain
conditions, they react to form photochemical
smog when subjected to sunlight. Carbon
monoxide does not react in the same way, but it
is toxic.
Honda Motor Co., Ltd. utilizes various systems
to reduce carbon monoxide, oxides of nitrogen
and hydrocarbons.
Exhaust Emission Control System
The exhaust emission control system is
composed of appropriate carburetor settings.
No adjustments should be made except for an
idle speed adjustment with the throttle stop
screw.
The exhaust emission control system is separate
from the crankcase emission control system.
Secondary Air Injection System
The exhaust emission control system consists of
a secondary air injection system.
The secondary air injection system introduces
filtered air into the exhaust gases in the exhaust
port. The secondary air injection system helps
improve emission performance.
No adjustments to this system should be made
although periodic inspection of the components is
recommended.
Crankcase Emission Control System
The engine is equipped with a closed crankcase
system to prevent discharging crankcase
emissions into the atmosphere.
Blow-by gas is returned to the combustion
muffler through the air cleaner and the
carburetor.
159
Technical Information