Complex sentence: By 1984, Nakamoto was already project leader on the design of the Honda RS125, RS250 production racing machines and by 1990 he had been moved up to the role of large project leader on both these machines.
Split into simpler sentences: By 1984, Nakamoto was already project leader on the design of the Honda RS125 and RS250 production racing machines. By 1990 he had been moved up to the role of large project leader on both these machines.