1999-2004 Honda TRX400EX FourTrax Service Manual, Page 27Get this manual
GENERAL INFORMATION
EMISSION CONTROL SYSTEMS
The California Air Resources Board (CARB) requires manufacturers to certify that their comply with applicable exhaust emissions standards during their useful life, when operated and maintained according to the instructions provided
SOURCE OF EMISSIONS
The combustion process produces carbon monoxide and hydrocarbonsControlling hydrocarbon emissions is very important because, under certain conditions, they react to form photochemical smog when subjected to sunlightCarbon monoxide does not react in the same way, but it is toxicHonda Motor Co Ltdutilizes lean carburetor settings as well as other systems, to reduce carbon monoxide and hydrocarbons-
EXHAUST EMISSION CONTROL SYSTEM
The exhaust emission control system is composed of lean carburetor setting, and no adjustments should be made except idle speed adjustment with the throttle stop screwThe exhaust emission control system is separate from the crankcase emission control system
CRANKCASE EMISSION CONTROL SYSTEM
The engine is equipped with closed crankcase system to prevent discharging crankcase emissions into the atmosphereBlow-by gas is returned to the combustion chamber through the air cleaner and carburetorCARBURETOR AIR CLEANER CONNECTING TUBE