2012 Sportsman 400/500 and EFI Tractor Service Manual 9923412, Page 137Get this manual
CARBURATION AND FUEL SYSTEM 500 H.OINTERNATIONAL EMISSIONS SYSTEM
Overview
International model ATVs are equipped with an emissions system from the factoryThe emission system is designed to meet the various international emissions standardsThe emissions system consists of: AAir Valve Filter BAir Valve Assembly (one way operation) CTubing DAir Injection Tube ECatalyst The emissions system utilizes an air valve filter (A), one-way air valve system (B), and vacuum to help reduce emissionsThe air valve assembly (B) contains vacuum shutoffWhen engine RPM drops quickly or is at high RPM, the air valve closesDuring idle through mid-range RPM the air valve is open and air is drawn into the from the PVT intake ductThe air valve assembly (B) opens and closes based on the vacuum pressure connected to the air ductThe exhaust pipe creates vacuum after each engine exhaust pulseThe air valve (B) opens and closes based on this engine pulseFresh air then travels through the air injection tubes (C and D) and into the exhaustThis air (oxygen) enters the exhaust pipe and mixes with the exhaust gases from the engine, reducing emissionsThe air and exhaust gas mixture then passes through the silencer (E), which contains catalystThis catalyst also reduces emissions by interacting with the exhaust as it passes through the silencerNOTE: No maintenance or service of the catalyst is required