The old-timers will remember WFO. Wide Full Open in mixed company, Wide F****n Open otherwise. Pre 1980, the carb's throttle slides were hooked directly to the twist grip. Turning the throttle to the max opened the slide full open. With constant-vacuum carbs, the diaphram pistons open in response to engine vacuum, not directly to the twist grip. With FI, the throttle blades open to computer witchery.