Keep in mind that around 1974-6 that some manufacturers made different setups for different markets, e.g. California. Cars that took regular and unleaded just had an air pump. Cars for unleaded fuel only had converters with or without an air pump. When unleaded fuel became commonplace and when leaded was eliminated, it became a nonissue, except in some parts of the world where it is still used. I also have been told that one of the side effects of these gizmos was to reduce the parts per million (ppm) of smog that came out, as the extra air duluted the exhaust mix and ppm of pollutants to air is how pollution is measured. So, either way, the automakers made Uncle Sam happy and saved the planet with the available technology. It wasn't until EFI came along that power, fuel economy and pollution control problems were dealt with effectively. BTW, if your air pump is making a clicking noise, you need to fix or replace it.