1933, JAP engine vs Harley Davidson engine. Huh, looks clear to me that HD was reverse engineering and or copying the JAP

 

In 1933 when J. A. Prestwich (J.A.P.) of Tottenham England, was soundly winning on the speedway tracks, Harley bought a JAP motor like this, and made their own version, retaining the Amal carb and Lucas magneto, according to Anibal