When determining the most successful miler of all time, Fred Nix, Scott Parker, Chris Carr, Ricky Graham, and Jay Springsteen come to mind. On the dirt, these legends are ferociously fast and fearless. But when it comes to the most successful flat tracker of all time, only one race machine comes to mind – the Harley XR750.
Produced from 1972 to 2008, the Harley XR750 (a.k.a. The Beast, Iron XR, 750 Sportster) is a dirt track motorbike hailed as the “most successful race bike of all time.” This legendary two-wheeler is literally and figuratively iron-clad and boasts a career with 29 AMA National Championship titles.
It did not matter that the iconic XR 750’s debut on the racetracks got delayed by two years. The bike was still effectively HD’s response to changes in the AMA Grand National Championship rules in 1969, which leveled the playing field for OEMs participating in the racing events.
Moreover, it was proof that the firm could step out of its comfort zone while ensuring American-made bikes do not lose their foothold in AMA competition.
The Quintessential Flat Tracker
The Harley XR750 is 3rd in the line of Harley-Davidson XL Sportsters and has the smallest displacement in the said series. It is the racing equivalent of the 1957 Haley-Davidson XL Ironhead and shares the overhead-valve (OHV) engine design and signature iron cylinder-and-head package with the rest of the bikes in the series. But do not let this lackluster description fool you.
“Accomplished” cannot begin to describe the competencies of this almost-liter-class bike. Not that it was the first 750-cc racer in Harley’s arsenal or the first ever to win a national event. If it were just about those two factors, the American firm has had other successful racing motorcycles – take the Sifton WRs/WRTTs of the ’50s, for instance.
What sets the Harley XR 750 apart from the other HD bikes is its insane count of winnings and association with racing legends and daredevil stunt performers. The motorcycle was practically part of the then-burgeoning careers of pro racers Cal Rayborn and Mark Brelsford and dirt-track titans Scott Parker, Chris Carr, and Jay Springsteen (AMA GNC winner for three consecutive years).
The bike itself has 29 AMA GNC titles (updated to 37 GNC and 502 premier-class main event victories, according to an April 2020 issue by Cycle World). Meanwhile, Scottie, Chris, and Springer collectively have 183 GNC main event victories, and 19 GNC wins under their belts.
Not Just for the Racetracks
To add, famed stuntman Evel Knievel’s custom 1972 Harley-Davidson XR-750 – made of steel, aluminum, and fiberglass and weighed approximately 300 lbs. – was used in 1975 to jump 120 feet over 13 Greyhound buses and, again, 133 feet over 14 buses five months later. This second attempt set Knievel’s personal best and a 25-year world record, only beaten by Bubba Blackwell in 1999.
A Street-Legal XR 750
Harley-Davidson only launched a larger-displacement, road-legal version of the XR 750 – the Sportster XR-1000 – in 1983, despite public demand. While you may think that only the displacement varied, it is quite the opposite. These two Sportster bikes shared nothing more than iron heads.
Ardent followers can only speculate whether or not this huge dissimilarity caused the XR-1000’s demise, as HD introduced yet another successor to the XR750 – the XR-1200 – in 2008.
Harley XR750 Specs & Features
The dirt bike comes to life via an air-cooled, 45° inclined V-twin 4-stroke OHV engine inspired by the XLR Sportster. The compression ratio is 8.5:1 but later on adjusted to 9.8:1 and 10.5:1. Similarly, the bore-stroke ratio is 79.4 x 75.7 mm (3.125 x 2.983 inches), tweaked to 3.1 x 3.0 inches after switching to alloy heads.
Piston displacement is 748–750 cm3 (45.6–45.77 in3), delivered by two 36-mm Mikuni carbs (each fitted with an air cleaner). Tweaked versions have exhausts mounted high on the left side of the motorcycle, away from the two carburetors.
Overall, this configuration lends to its 115 mph (185 km/h) top speed rating and 73–82 hp (53.7–60.3 kW) @ 7,600–7,700 RPM horsepower – with approximately 87–100 hp (64–73.5 kW) @ 7,800 RPM for post-1972 alloy-head versions, including the XRTT variant.
Hill climbing enthusiast Lou Gerencer’s custom 1989 Harley XR750 equipped with NOx and mechanical fuel injection was estimated to spew up to 150 hp (110 kW).
The then-new OHV racing mill was adopted from the Sportster XLR with a detuned displacement (the XLR had a 900-class engine). It featured Bill Harley’s four-camshaft design, with each push-rod allowing for optimal rocker arm operation. Furthermore, the layout “enabled fine tweaking of the cam timing” and lent to improved durability and overall performance.
Despite the stable setup, the new engine did have one flaw – cast-iron cylinder heads that made the mill prone to overheating, earning it the infamous nickname “waffle irons.” These alloy heads put the XR750 at a disadvantage in long-distance events, especially when racing conditions were not cool.
HD eventually changed the cylinder heads to aluminum to reduce the engine’s propensity to overheat and paired them with larger cylinder valves for more effective cooling. With these adjustments (and after completing 200 homologated units), the XR750 finally debuted at the Colorado Springs National on April 30, 1972 – a little over two years since it was initially approved for Class C competition by AMA.
Fuel & Lubrication
The fuel tank capacity for the XR 750 is 9.5 L (2.5 USgal) of high-grade premium fuel due to its high compression ratio. Lube-wise, recommended oil quantity is 2.6 L (2.75 US quarts). The motorbike’s power mill was assembled with Bel-Ray MC-5 SAE 40 Engine Oil.
Unlike previous HD racing models, the firm advises against mixing this lubricant with a Castor-base oil unless the oil tank and reservoir have been completely drained and rid of old engine oil.
A 4-speed manual transmission and a multi-plate, cable-operated dry clutch assembly deliver power to the ground. Meanwhile, triple-row chain primary drive handles wheelspin. The two-wheeler’s initial 4-speed manual transmission (said to redline at 8,000 RPM) got upgraded to a 5-speed gearbox with accompanying changes to compression in 1978.
These alterations did nothing but improve the superb handling characteristics of the XR750 one bit, as the bike delivered power and hooked up to the tracks whenever it mattered.
The Harley XR750 has a Fairbanks-Morse Single-Fire Magneto ignition system. It did not have the solid-state generator/regulator that earlier WR bikes had but shared the same magneto control twist and rotator control plates with the latter. The ignition timing is set to 33° to 35° BTDC.
The XR 750 is factory-setup with Champion N6OR spark plugs but can be changed to Champion N57G plugs for racing applications. As for the battery, there is none specified in the owner’s manual, although the liter-class Sportster did accommodate a 12V 20 Ah/(10 HR) GYZ20H battery (view on Amazon). Check with your nearest dealer if this format can be fitted in the XR750. Otherwise, ask to be pointed in the right direction.
Tires & Brakes
Factory knobbies consist of 4.00 x 19 Goodyear tires (front and rear) mounted on spoke wheels/aluminum rims. A rear disc brake (no front brakes and corresponding levers) completes the two-wheeler’s tire-and-wheel assembly and provides the bike with its spectacular halting power.
A KR-style swingarm chassis (a.k.a. Twin-loop full cradle) with Ceriani forks and dual Girling rear shocks houses the engine and tire-and-wheel assembly of the Harley Davidson XR 750. The caster angle is 26° ± 30′ with a trail length of 87 mm (3.437 inches), while the wheelbase is 1,441.45 mm (56.75 inches).
Turning radius and ground clearance are unspecified in-service data references online and is best checked against the service manual. The same goes for wheel travel by these suspension units.
Overall dimensions are 83 x 33 x 31 inches (2,110 x 840 x 790 mm – L x W x saddle height) for Harley XR750s sold between 1978 and 1980. There would be slight variations in length, width, and height across different markets and model years of the dirt tracker. Depending on the incarnation, dry weight ranges from 295 to 312 lbs. (or 133.8 to 141.5 Kg).
Its 1972 race version sported an orange-and-black bodywork (better known as Jet Fire Orange) and peanut-shaped tank, had clean handlebars (not overcrowded with too many switches and controls), offset, staggered footpegs, and a Smiths tachometer for instrumentation.
Except for minor cosmetic tweaks here and there, this spartan styling is carried over to the rest of the bike’s iterations until its outgoing year in 2008.
The revered motorcycle that the “titans of the XR750” rode is not to be confused with the full-faired XR-TT 750, with its aluminum tank and leather pad.
’86–’93 Evo Sportster 1200s are great donor bikes if you want to make a close-to-the-original replica of the ’70s XR750. Some parts may need to be made from scratch. But there are still one or two outfitters with OEM parts that can be tweaked and used instead of stock components.
Online search results give rebuilders tips on how to bring out the optimum performance of the famous motorcycle – with embellishments like Works Performance shocks, USD Kawasaki Ninja, or Marzocchi forks (view on Amazon), a Champion swingarm, and the like.
How Much Is an XR750 Worth?
For reference, the non-exhaustive table below consolidates retail and trade-in values of all Harley-Davidson XR750s released in the U.S. (source: Nada Guides). The original MSRP for the 200 homologation units produced in 1972 was $3,200 – approximately $22,000 today, with inflation factored in. As complete references are hard to come by, I have opted to exclude MSRP data for the rest of the incarnations to ensure accurate pricing is shared:
|Model Year & Trim
|$40,080 – $7,055
|$49,200 – $10,270
|$35,055 – $8,950
|$35,055 – $8,950
|$37,570 – $9,150
|$45,845 – $9,510
Auction listings for the 750-cc Harley range between $8,250 and $69,000 (at least for those with prices disclosed). Most resale units are post-1972 models with little-to-moderate cosmetic damage and great working conditions.
Some are more prestigious than others – examples include a ’95 XR750 with a custom frame built by Joe Kopp’s father, autographed by Chris Carr and Kenny Tolbert, and last ridden at the New York Vernon Downs Mile by none other than Chris Carr himself, and a 1972 “alloy head” XR750 sold by Dave Camlin to AMA Hall of Famer Bob Hansen.
Other noteworthy auction listings are as follows:
- Car and Classic: £55,000 (approximately $69,000) in Germany
- 1980 XR750 (personal bike of Eddie Dodge), Hemmings: $49,000
- Smart Cycle Guide: $15,000 (restored) and $35,000
- 1977 Harley Davidson XR750: $28,871
In restoring a not-so-dilapidated XR 750, prepare to spend at least half of the cheapest auction listing above. New port heads, OEM lifter blocks, primary covers, and the peanut-shaped fuel tank alone would already amount to $6,300 (sourced from eBay). Expect to have higher expenses if you consult a professional vintage/racing outfitter.
The AMA Grand National Championship
The AMA National Championship was the leading motorcycling tournament in the U.S. from 1954 until the late ’70s. Its flat track series consisted of five competition segments: dirt track or mile, half-mile, short-track, TT steeplechase, and road races (source: Wikipedia).
Flat track events were the most celebrated of the lot – partly due to the rush it gave spectators and largely because American bikes were always at the forefront of these races.
Harley-Davidson motorcycles dominated the said series since its incoming year, with Joe Leonard becoming its first AMA grand national champion. These bikes’ high-quality build and splendid performance were a lethal combination, which left other motorcycle manufacturers little to no shot at the coveted title.
It was generally accepted that HD would forever be undisputed in these racing circuits – well, except for the Brits. They constantly complained to AMA about the disparity in allowable engine displacement between OEMs. They had good reason to complain since rules governing AMA tournaments seemed to prevent overseas motorcycle firms from winning.
Rule Changes Affecting the 1969 Season Onward
So, in November of 1968, the tournament’s Competition Committee finally let go of the 1934 “equivalency formula” and permitted all OHV two-wheelers used in professional amateur and expert dirt track races to have 750-cc piston displacements the same way that side-valve machines did.
This new ruling eliminated the 50% engine-size advantage American-made motorcycles such as Harley’s award-winning KR bikes previously had. Flat track participants were the first to enjoy this change, succeeded by road-racing wheelers the following year. Brakes were also allowed for the first time in dirt track events.
The circumstances gave Japanese and British firms their first true opportunity to make their mark in the American-dominated sport. It also gave Harley-Davidson the needed push to answer the call of the times and develop its own OHV-engine powered racebike – hence, the Harley XR 750 was born.
Harley-Davidson, Inc. (a.k.a. HD, Harley) is an American manufacturer known for badass, custom bikes and racing motorcycles like the Harley XR750. The Milwaukee giant was founded in 1903 by William S. Harley and the Davidson brothers (Arthur, William, and Walter).
They initially produced their motorcycles in a machine shop owned by friend Henry Melk. From a failed first attempt at a 116-cc motorized bike that took two years to create, Harley is now a global powerhouse boasting premium-quality motorcycles, a cult-like following, a tumultuous history, and an über successful track record.
Conclusion – Harley Davidson XR750 Review
With its half-century reign in the AMA GNC competitions (and elsewhere), everyone can agree that no words truly give justice to the XR750’s worth. After all, the iconic 750-class motorcycle has proven itself to embody many ideals – among them a firm resolve, grit, and passion.
And while these values are not exclusive to Harley-Davidson, they are best manifested through the prowess and limitless potential of the XR750 that continue to dominate the racetracks and hearts of dirt-track enthusiasts.
Kris is an avid off-roader and outdoor enthusiast who loves to brave the elements and take on challenging terrain. He also enjoys sharing his passion and knowledge with others so that they, too, can appreciate the ride.