Leaded fuels were known to be a health risk and unleaded fuel was introduced into Australia in 1986. In a further effort to reduce emissions, catalyctic convertors were added to the exhaust system and exhaust gas recirculation and air injection systems were also added. Even fuel evaporation was shown to be a bad source of air pollution so modern engines included an evaporative control system.
The wide spread use of fuel injection systems also gave engineers a much more accurate way to control how much fuel is burnt on each stroke of the engine. This has allowed more precise ignition timing and electronic ignition, more precise fuel metering, and computerized engine management.
Further developments in engine design have also helped so that the humble piston engine is a far more efficient than it was in the past.
Faults in these emission systems can occur from time to time and we regular check these systems during servicing.