Yamaha Power Valve System. The thing that made the Yamaha RD350YPVS go like shit off a stick from about 6000rpm upwards.
Well, Brian, it's the YPVS that makes this bike so special.
RD350YPVS - 1980's 2 stroke sportsbike, successor of the LC and mighty fine in it's day.
Now collected by strange men with a passion for rooting in oily boxes at autojumbles.
He had a 'valve, but it shat itself.
Did you see that slapper - I nearly shat myself.