A boost bottle is an empty chamber that is used to store vacuum. When your engines running and you close the throttle, the piston sucks most of the intake mixture out of the bottle (leaving a vacuum). As soon as you open the throttle again , the bottle naturally tries to refill itself (thru the carb), thus pulling more air and fuel for an instant. More air and fuel should = more power or better throttle response. I made mine out of a sharpie marker cut in half, with the end sealed off.