Complex sentence: In 1931 he won the Belgian Grand Prix and he won the Grand Prix de la Baule three consecutive years from 1931 to 1933 but after that his career waned and he was out of racing by the latter part of the 1930s.
Split into simpler sentences: In 1931 he won the Belgian Grand Prix and the Grand Prix de la Baule three consecutive years (1931 to 1933). Then his career waned and he was out of racing by the latter part of the 1930s.