in 1939, a 4 cycle 1.5 hp motor was made to be bolted onto a Schwinn... and the Whizzer was born

During the beginning of World War II, Whizzer faced challenges but ultimately gained government approval to continue engine production by highlighting the Whizzer as essential transportation for defense workers. 

This led to the exclusive "New Model" engine designed solely for defense workers.

and there was a Roy Rogers Whizzer too

https://justacarguy.blogspot.com/2018/04/roy-rogers-brand-whizzer-thanks-steve.html

https://www.audrainautomuseum.org/colors-the-cars-of-summer/1955-schwinn-whizzer-model-wz-1955-motorbike