 The 76 types are of die-cast zinc construction and were introduced in the early 1930s, replacing the earlier 6 series, which were of bronze construction, although basically the same design.The 276 type was introduced in 1940 in an attempt to improve the carburettor's durability in dusty and dirty operating environments.In the same design range were the 4 and 5 types with smaller bore sizes and the 29 type with larger bore sizes.