The typical small two-stroke engine has two big problems that cause hilariously bad emissions: 1) The lubricating oil is mixed into the fuel and burned in the

The typical small two-stroke engine has two big problems that cause hilariously bad emissions: 1) The lubricating oil is mixed into the fuel and burned in the combustion cycle. The combustion products of this oil are not clean. 2) They combine exhaust and intake into a single "stroke", i.e. the downstroke after ignition, which can result in unburnt aerosolized fuel escaping with the exhaust. Additionally, fuel injection systems can typically achieve better emissions than carburetors can. AFAIK small two-strokes (and some four-strokes like small outboard motors, etc.) are largely the last bastion of carburetors in engines manufactured today.