No, the Honda CB400F is not the only Japanese motorcycle from the 1970s to have been built with a 4-1 exhaust system as standard. While the 4-1 exhaust system was indeed a distinctive feature of the CB400F, there were other Japanese motorcycles of that era that also came equipped with a similar exhaust configuration.
One notable example is the Suzuki GS Series, particularly the Suzuki GS750 and GS1000 models. These motorcycles featured a 4-1 exhaust system as standard, which contributed to their performance and distinctive sound.
It's worth mentioning that exhaust system designs can vary across different models and years within a manufacturer's lineup. While the 4-1 configuration was popular during that era, there were also motorcycles that utilized different exhaust layouts, such as 4-2-1 or even 4-2 systems.
If you have a specific interest in motorcycles with a 4-1 exhaust system, it can be worthwhile to explore various models and years from different manufacturers, as exhaust configurations can be a distinguishing feature that contributes to a motorcycle's performance, sound, and overall character.