Yamaha invented the boost bottle system.
On June 30, 1980, Yamaha announced a new engine system technology that it had developed independently: the Yamaha Energy Induction System (YEIS) for 2-stroke engines. YEIS was first used on the YZ motocross models in 1980, then on four other 2-stroke models in 1981.

Significant performance gains were realized with this!

A lot of folks removed this thinking it had to do with emissions!

This IS NOT an emissions to meet smog deal!