Below is a picture of one of my favorite machines.  I've got lots of favorites, but this one ranks right up there.  Its a 1930 Harley-Davidson CA Peashooter Factory Racer.

To me, this bike represents the bare bone's approach to racing, and the special factory efforts to get ahead of the competition.  The bike is a 500c.c. Overhead-Valve "Peashooter", featuring direct drive, single-speed countershaft.  Peashooters were built in 350 and 500 cc versions, this one being the only known 500 in this configuration.   Notice how the gas tank is notched right above the motor?  This was to fit in the taller cylinder that came on the "factory built"  500s.  Harley-Davidson did offer a kit to make your 350 a 500, which included stroked flywheels, different connecting rod, different piston and cylinder.  The kit was often put to use by privateers, who would have to home-modify their frames for the taller engine.  This example was built at the factory this way, and also features special, stronger frame which fits the 500 motor.

Harley began production of their 350 OHV motor during the 1926 model year, having debuted the technology on the track toward the end of the 1925 racing season.  The nickname "Peashooter" quickly stuck, given for the machines "pop-pop" sound, and before long, the new machines were doing more than just holding their own on the track. 

Before long, 500cc versions of the same engine were being stuffed into low slung race chassis, with riders like Joe Petrali, Jim Davis and Lou Balinski competing for top honors on dirt ovals around America.  By the early 1930s, despite some of the toughest economic times the Motor Company had ever seen, the developement of the Peashooter had brought Harley-Davidson checkered flag after checkered flag, and numerous national championships to boot.

A perfect combination of power, art, and the vision that has brought the motorcycle world to where it is today!