Yes, Harley-Davidson has produced 4-cylinder motorcycles in the past. The most notable example is the Harley-Davidson VR1000, which was a superbike developed for racing purposes. The VR1000 was powered by a liquid-cooled, 996cc V-twin engine with four valves per cylinder. It was specifically designed for competing in the Superbike World Championship in the 1990s.
While the VR1000 was a significant departure from Harley-Davidson's traditional air-cooled V-twin engines, it represented the company's foray into the world of high-performance sportbikes. The VR1000 had limited success in racing, but it remains an important part of Harley-Davidson's history as their first attempt at a 4-cylinder motorcycle.