The XR-750 would be utilized in a variety of racing through the years. Even the onslaught of Japanese machinery had a tough time overcoming wt talents of the XR-750, mainly in part to M low weight and terrific power. Eventuallj| the duty of the legendary XR-750  eclipsed by more modern equipment,

From the moment the AMA’s Grand National Series began in 1954, the Harley wrecking crew had dominated it. In the first 13 years of the series, Harley-mounted riders won the championship 12 times.

But then came the late ’60s, and the competition from Great Britain got a lot tougher. From 1967 through 1971, Harley won the title just once, while Triumph and BSA combined for four victories. The engineers from Milwaukee were scrambling.

The company introduced one new racing machine, designated the XR750, in 1970. Based on the company’s Sportster streetbike engine, it was clearly a stopgap measure. By 1972, its successor was ready. And although it was also called the XR750, it was another animal entirely.

This machine, which became known as the “alloy XR” to differentiate it from the previous iron-barrel XRs, was an instant success. That season, Harley factory racer Mark Brelsford rode his XR in 15 dirt-track races, winning three and finishing in the top five 11 times. By the end of the year, Brelsford won the Grand National Championship going away over a rookie by the name of Gary Scott.

But that’s only the beginning of the story. In the 27 seasons since then, alloy XR engines have powered championship-winning motorcycles 20 times, leaving only seven titles for the rest of the world. And if you go to a Grand National Dirt Track Series race today, chances are the winner will be riding an XR Harley.

Motorcycle-USA review

I've got to be honest about this article. In normal circumstances, I would rather be guest of honor at a speed camera (radar) operators' Christmas party than ride a Harley. Fat, slow concrete mixers with tassels and nine headlamps do not excite me. But there is an exception - the XRTT Harley-Davidson road racer. For me, the XR has always been an icon of racing.

The reason for my life-long love affair with the XRTT is the Anglo-American Match Races. Conceived as a publicity vehicle for BSA Group Triples, the races were dominated by British riders and British bikes. Nearly, if not for a kind and achingly modest Californian called Cal Rayborn who rode an XR Harley.

I remember being on the inside of the Esso hairpin at Oulton Park one filthy wet spring day. Sleet was falling miserably and patchy fog finished off the picture. Out of the mist came a gaggle of Triples led by Ray Pickerell who was always hard on the brakes. Rayborn was about seventh. The surface was atrocious - beyond impossible for hard braking. Rayborn eased up the inside of the pack with the delicacy of a ballet dancer, squeezed the Harley through on the inside of Pickerell and the booming Twin accelerated away into first place to the screams of the crowd. If I had just witnessed Moses parting the Red Sea I couldn't have been more impressed.

The truth was that a lot of the XR's performance in the Match Races was due to Rayborn himself, who was later tragically killed in New Zealand preparing the for 1974 GP season on an RG500 Suzuki. What the XR excelled at, and still does, is the fiercely competitive mile and half-mile dirt track races that are the backbone of professional motorcycle racing in America. As a road racer, the two-valve, push-rod V-Twin was too little too late by the time of its introduction in 1972.

The first XRTTs had - bizarrely - cast iron heads and barrels. To describe them as a disaster is putting things at its best. The engines overheated, they made less power than the side-valve KRTT that they replaced and the gearboxes were fragile. Harley star, Mert Lawill noted: "Agony. That's the XR. That thing took 10 years off my life."

Still, it was development of this early XRTT, tuned by Walt Faulk, that enabled Rayborn to win three of six 1972 Anglo-American Match Races.

In 1972, Harley re-launched the XR with a motor so new that it really ought to have been given a fresh designation. Harley designer Pieter Zylstra had drawn the motor almost three years earlier, but in those days development was a slow process, not aided by the fact that Harley was in dire financial trouble and struggling for existence.

The new engine featured twin carburetors, alloy heads and alloy barrels, but retained the original 45-degree angle, two-valve configuration. Pushrods were still used to keep the motor short and the cylinder heads light - both important factors in dirt races where the center of gravity is critical.

From the outset, things were dramatically better. The best of the side-valve engines and the early "waffle-iron" XR push-rod motors gave around 64 horsepower. The new motor produced 73 hp straight from the drawing board and revved to 8200 rpm with comfort. Interestingly, current well-tuned XR engines are giving over 90 hp, which is not bad for a two-valve 750!

The XR went on to dominate American flat track racing - and still does today. As a road race machine, it should have faded into obscurity but didn't. Enter Keith Campbell's Hourglass Racing - guardians of the XR pavement racing flame.

Ever since those heady days of the Anglo-American Match Races I have dreamed of riding a road racing Harley, but not many opportunities to do so come up in one lifetime. For a start, only a handful of road racing XRs were ever built. The figures vary between 15 and 25 depending who you speak to, and of the few that were made most were destroyed in action; the rest reside in museums.

While most XRs live in cocooned luxury, two don't. These belong to Georgia car dealer, pilot, bike racer and Harley-Davidson enthusiast Keith Campbell. As a hobby, Campbell owns and leads Hourglass Racing. The bikes are tuned by Carl Patrick in Ohio who is considered to be the world's best XR tuner - bar none. 

The bikes are priceless - there's no other word for it. If they did come on the market, think perhaps $125,000 each and you wouldn't be far out. So how do you get a ride on America's most desirable classic racer? Well, you need a giant slice of luck. In my case it came through being parked next to Hourglass Racing when I was competing on Eric Kalamaja's Suzuki Proddie racer at the Roebling Road races in October.

I had spent two days making big eyes at the Harleys like a teenager in love. When I mentioned that I would love a ride on one of the big black and orange beasts to crew chief Joe Brown, I was met with a gunfighter hard stare and the conversation crunching comment that: "No one rides our XRs!"

Well, that should have been a strong enough hint, but then I got talking to Campbell. Could I have a ride on his XR? "Sure, get right aboard." It was a simple as that. Even though Campbell was relaxed about me riding his XR, Joe gave me a look which unmistakably spelt out that if I dropped their baby I was likely to go back to Britain in a body bag.

Looking at the XRTT brought on mixed emotions. First, Campbell's Harley is ten steps beyond immaculate; it is literally in show-winning condition. But to the practiced eye it is readily apparent that it is a serious racing machine, too. One look at the heavily scrubbed Avon racing tires showed that Campbell rides the bike on the limit. The XR also looks immense. To protect the motor, huge air filters are fitted. These, combined with an apparently enormous humped tank that sits on top of the V-Twin's cylinders and the high-backed 1970s seat, make the bike look intimidating. Compare the bike to a Triumph triple, which was the Harley's most direct opposition at the time, and the British bike has a mean, lean, tight and nimble look. By contrast, the Harley seems to stick out everywhere.

But there is a magical transformation the moment you are in the saddle. The bike seems to mold round the rider in a quite miraculous way. Instead of the ungainly and bulbous lump you have just been looking at from the outside, the XR feels narrow, tight and compact; just perfect for serious racing. It's not just a feel-good factor, either. The XRTT weighs in at around 320 lbs., and that's not much heavier than a well-sorted BSA triple.

From the moment the feather-light clutch is engaged, it becomes apparent that this is like no other Harley you have ever ridden before - or are ever likely to ride again. The motor pulls like a train, which could be reasonably expected, from a 750cc V-Twin. What comes as a shock is its smoothness. Normally, a Harley will detach your retinas if revved hard, but not an XR.The 79mm x 76mm Twin is wonderfully smooth running like a turbine all the way up to the redline at 8200 rpm. This is almost 2000 rpm more than a road bike and then there's another 800 rpm left for last-lap emergencies.

What it lacks is a decent gearbox. There are only four ratios, and the gear pedal travel is enormous. Keith assures me that one becomes used to it, but in the short time I rode the bike it was a constant distraction from the pleasures of the rest of the bike.

The handling is a carbon copy of the motor - ultra smooth, neutral and so encouraging. Roebling is not the smoothest track in the world but the XR deals with it effortlessly. With a short 54-inch wheelbase and a steering head angle of 24 degrees, the bike is nimble and turns with complete neutrality. The Harley can be fed into corners with laser precision.

Keith's XR is based closely on the original XRTT chassis that was built in chrome-moly by Nickels Engineering. It doesn't have the classic elegance of a Rob North or Seely frame, but there's no doubt that this is a fine chassis. On Roebling's fast and bumpy, sweeping bends, the XR was rock steady and crying out to be raced hard.

Keith has fitted twin Ceriani discs to the XR which are period and honest, but it would have been nice to see the original 4ls Ceriani front brake. By 1972, Harley's best road racers, Rayborn and Renzo Pasolini, had moved from the big drum brakes to discs and you can soon see why. Two fingers on the front brake and Campbell's XR scrubs off speed like hitting a giant pillow.

All too soon, the marshals were flagging us for the end of the session and I was genuinely sorry to have to return the bike. I've been racing a long time and ridden many fine bikes, but very few have provided as much satisfaction as the Keith's XR. What wouldn't I have given to have free rein in a race, rather than a practice session, where I could have been less cautious and respectful of a bike which truly aches to be raced? Can Santa come for my birthday as well as Christmas?

1972 Harley Davidson XRTT Specifications:
Engine: 750cc, two-valve, pushrod V-Twin
Gearbox: 4-speed, right-hand shifter
Chassis: Chrome-moly 4130 by Nickels engineering
Weight: 314 pounds
Wheelbase: 54 inches
Top speed: 145 mph

Source Motorcycle-USA