Is the orifice smaller than the inlet? Might not be drawing as much vacuum e as you think.I contacted ftz racing and they said it's for a fuel pump that works off a pulse. I would think it would run like crap if it's open but it doesn't.
Come to think of it, I do have this device on my WR500. Yamaha ENERGY INDUCTION.in olden days some 2st had a surge bottle on the side of the motor. It would charge with fuel when off throttle and at high rpms. Then when you opened the throttle it would suck in the extra fuel/air mix for an initial go fast charge of fuel. Didnt last but a few years. Maybe this is what it is for.