while someone pushes the pedal HARD, check all along every brake line / fitting / seal for any wetness with bright torch.
check ur available pedal travel is sufficient for the new calipers during bleeding.
ie when nipple open, measure the pedals travel from full rest to fully down (that's ur total MC travel).
now after fully bleeding the system, push the pedal down hard as u can with engine on and measure the pedals position.
if the pedals already travelled over 4/5th down the available travel, it ain't pumping enough fluid cos it's too small, especially once everythings red hot & spongy on track.
