Whizzer motorbikes differ from modern bikes because most were not purpose-built motorcycles, but rather combinations of a standard bicycle with a separate piston engine. Whizzer motorbikes are more similar to modern motor scooters or mopeds than they are to either modern motorcycles or bicycles.
Most of the history of Whizzer motorcycles dates to the early and middle parts of the 20th century. The brand was first introduced to the bicycle market in 1939 by Breene-Taylor Engineering. While they would eventually become most famous for producing Whizzer motorcycle engines, Breene-Taylor actually began its life as an aircraft parts manufacturer. The earliest Whizzer engines were not very powerful, supplying just over one horsepower. Like other contemporary motorcycle engines, Whizzer engines were manufactured exclusively in cast iron, making them extremely heavy. Eventually, Whizzer began using aluminum to manufacture their engines, making them much lighter and less prone to overheating.
Due to competition from other companies selling motorized bicycle kits, Whizzer introduced the Pacemaker, its first complete motorcycle, in 1948. That year was the high watermark for the Whizzer company, as it maintained 12 warehouses across the country, while selling over 10,000 engines annually. The original Whizzer company ceased operations in 1965, as it was unable to keep pace with competitors. A completely distinct company calling itself "Whizzer U.S.A" produces modern replicas of original Whizzer motorcycles.