The Specs: The XR is powered by a 750cc overhead valve racing engine with aluminum cylinders and heads. The compression ratio is 10:1. The transmission is a 4-speed that is integral to the engine cases. Fuel and air is mixed in a pair of 36mm Mikuni carburetors and exhaust exits through tuned dual reverse cone megaphones. It also has Ceriani front forks, and Girling racing rear shock absorbers. To reduce weight the 2½ gallon fuel tank is fiberglass as well as the rear seat/fender combo. This XR set up for dirt track racing is not equipped with brakes. It rides on Akront aluminum rims and 4.00 x 19" dirt tires.
The first XR was created as a stop-gap for the 1970 racing season in which a rule change allowed 750cc overhead valve engines to compete in the Grand National Championship series previously dominated by 750cc side valve engines only. Work began on creating a specific race version 750cc overhead valve engine to replace the 1970 model. The result was the 1972 XR750 with aluminum alloy heads and cylinders rather than the previous cast iron type. The alloy heads were lighter and had better cooling properties than their predecessors. The XR remained virtually unchanged for the next 17 years outside of a redesign in the oiling system in 1975.