XTreme XRs

XTreme XRs
XTreme XR's: A Milestone Motorcycle Still Chewing up the Miles

Story by Paul Garson, 1/22/04

Milwaukee's Racebred XR

	Here's the x-iest of the XRs... first off the H-D hand assembly line.

For some 34 years running, the XR750 has been the ultimate "do it in the dirt" warrior, its victories literally spanning decades and dirt (and paved) tracks across the country, both in the hands of factory-sponsored pro's and independent riders as well. Introduced in 1970, the XR750 took over where the vaunted KR-TT's left off. Its first couple years, run with iron barrels, were problematic, but when fitted with aluminum cylinders and cylinder heads the new factory racers found their stride. Equipped with Ceriani forks and Girling racing shocks, the engines were stuffed into welded, tubular 4139 steel frames, its aluminum spoked wheels shod with Goodyear rubber. While the early ironhead design, basically a destroked 880cc Sportster, made for 70 hp, the aluminum upgrades, combined with polished valves, pistons and cams, chromed valve stems, and compression bumped from 8:1 to 10.5:1 brought out 20 more ponies, the XR's cranking out 90 hp in a bike that tipped the scales at 290 lb. Dual 36mm Mikuni's fed the hypo-ed Sporty motor, a 4-speed tranny shifted through a dry clutch and spark was provided by a Fairbanks-Morse magneto. You could have any color you wanted as long as it was Jet Fire Orange. Its lightweight precluded a starter of any kind, so it's a hump and bump roll-on to get it fired up.

Once fired up, you'd better get a grip. Think of a stump-pulling torquey, pit bull tough, light as a butterfly/sting like a million bees bike and you've got the gut feeling of riding an XR. Only one-quarter turn on the throttle goes from nada to WFO and it pulls without letup from 2000 rpm on up the scale and off it. While there's a rear disk brake, riders usually relied on engine compression to bring the bike down to non-warp speeds.

It should be noted the initial design for the XR750 is credited to a Dutchman by the name of Pieter Zylstra, and the first factory bikes tended to overheat, earning the less than favorable moniker as the "Waffle Iron." It was the legendary Cal Rayborn who brought the XR its first fame. Riding a Walt Faulk prepped bike, he won three out of the six British-American "Transatlantic" races. Not content with mere roadracing, Cal piloted an XLR-engined streamliner to a land speed record of 265 mph at Bonneville. Sadly, Cal died in a 1974 crash aboard a Suzuki at age 33. Later Team Obsolete would campaign Cal's XR750.