The RC30 had used 38 mm constant velocity carburettors which, for road use are quite nice, maintaining a high air velocity across a wide rpm range, though were not as well suited for racing. The RC45 did away with carburetors and in their absence a brace of four 46 mm throttles were replaced, Honda now had the throttle area it needed to make big horsepower at high revolutions.
The RC30 used 38mm constant velocity carburetors, which are good for road use because they provide a consistent airflow across a wide range of engine speeds. However, these carburetors were not as effective for racing. The RC45 eliminated carburetors and replaced them with four 46mm throttles, giving Honda the necessary throttle area to generate high horsepower at high RPMs.