A variety of embodiments of exhaust systems for engines including small off-road engines, and related methods of operation, are disclosed. In at least some embodiments, the exhaust system includes a first conduit that receives exhaust emissions from a first engine cylinder, and a second conduit that communicates air to a first port on the first conduit. The air mixes with the exhaust emissions within the first conduit so as to produce a chemical reaction, and a level of at least one undesirable component of the exhaust emissions is reduced. Further, the exhaust system does not include any catalytic converter. In some embodiments, the exhaust system further comprises a crankcase ventilation system.