Exhaust emission control systems try to prevent excessive pollutants from escaping into the atmosphere from the vehicle's exhaust output. Many of the 1949-69 models do not utilize any emission control devices or systems at all. On these vehicles, as well as on vehicles equipped with emission controls, one of the best methods for preventing your vehicle from polluting excessively is to keep the engine running as efficiently as possible. Performing the maintenance and tune-up procedures in and 2 regularly will help your engine to run as efficient and cleanly as possible.1949 to Early 1967 Models
With the exception of the thermostatic air cleaner, these vehicles were not available with any exhaust emission control systems or devices.Late 1967 to 1969 Models
Along with the fuel injection system available on some of the type 3 models, which is designed to reduce exhaust gas emissions, only some carbureted models manufactured from August 1967 to 1969 (engine No. H 5 000 001 and newer) were equipped with an additional control system. This system, which is referred to by Volkswagen as the Exhaust Emission Control System (EECS), is comprised of a specially tuned carburetor, a throttle (valve) positioner and a vacuum advance/retard canister attached to the distributor.THROTTLE (VALVE) POSITIONER
Carbureted Volkswagen models equipped with the EECS utilize a throttle valve positioner. This device attempted to reduce exhaust emissions by automatically adjusting the throttle closing rate. By controlling the rate the throttle closed, the positioner avoided an over-rich condition in the engine, which causes a large amount of unburned fuel (hydrocarbons) to exit into the atmosphere through the exhaust system. Some models also came equipped with a dashpot to supplement this positioner.VACUUM ADVANCE/RETARD CANISTER
A vacuum advance/retard canister was used on models equipped with the EECS. This mechanism was designed to advance or retard the ignition timing depending on the engine vacuum, which changed according to engine speed and load. Changing the ignition timing affects exhaust gas emissions; therefore, by changing the timing according to engine speed and load the exhaust emission output could be fine tuned.1970-81 Models
While Volkswagen vehicles manufactured from 1970-72 were equipped with the Throttle (Valve) Positioner, 1973-81 models were equipped with a different system designed to limit the amount of harmful exhaust gases from the engine. This system is described here to further general automotive understanding of emission systems.EXHAUST GAS RECIRCULATION (EGR) SYSTEM
Instead of utilizing a throttle valve positioner, some 1972-73 models and all 1974-81 models use an Exhaust Gas Recirculation (EGR) system to lower exhaust gas emissions. The EGR system lowers the emissions by diverting a portion of the exhaust gases back into the intake manifold below the carburetor. This dilutes the incoming charge of fuel and air. Since the recirculated exhaust gases are largely non-combustible, and since these gases dilute the incoming air/fuel charge, the exhaust gases restrict the amount of burnable intake charge allowed into the cylinder for combustion. Also, since the incoming exhaust gases are noncombustible, the exhaust gas does not appreciably affect the air/fuel mixture. Since the incoming air/fuel charge is diluted, combustion is maintained at a lower temperature, which reduces the formation of oxides of nitrogen.
None of the 1949-69 Volkswagen vehicles are equipped with this system; this description is only for general information on exhaust emission controls used on 1973-81 models.