Probably an elementary ? for you old timers. Got the rebuilt YH in & the Corsa runs great.Fires up in a coupla cranks, few more when hot. No complaints in normal aspiration.However, when the turbo kicks in above 35K it pings like a S.O.B. Running 91 octane. New plugs, new fuel filter.Retard the timing?? What am I missing? TIA. Scott '65 Corsa UNSAYF