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The two-stroke experiment

Kawasaki 750 H2R dirt tracker

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In the American flat track sport, Harley-Davidson’s XR 750 was always boss in the ring. It could have turned out differently, however: In the mid-1970s, angry two-stroke engines wanted to end the supremacy.

Kawasaki 750 H2R Dirt Tracker (Part 1)

B.The first example that clocks tick a little differently in the USA than in the rest of the world is motorcycling. Shortly after 1900, when the racing started, wooden arenas were built across the country. In these motor races, each with two steep wall curves inclined up to 60 degrees, daredevil guys thundered over unplaned wooden planks on special 1000cc racing machines without clutch and gearbox and without brakes with over 200 things. The spectacle was spectacular, attracting thousands of visitors like a magnet, but cost a huge toll. Serious accidents and deaths were the order of the day. As the successor to the "Neck and neck with death" board track races, the dirt track or flat track races established themselves on flat oval courses. The tracks were a quarter, half, or a full mile long. Things really got going after the Second World War. 

From 1954 the AMA, the American Motorcycle Association, introduced the "Grand National Championship". The championship was divided into three categories: Flat Track, TT, a kind of motocross and thoroughbred street racing. The best driver was celebrated as the “Grand National Champion” at the end of the season. The title was the highest rating that a US racing driver could achieve – from an American perspective, more valuable than a title in the road world championship.

The races were hugely popular and the professionals made good money. The flat track runs were particularly popular. The oval of the rolled clay roadway covered with oil sand was perfectly manageable for the audience. The enthusiastic fans were able to follow the start, driving style, battles for positions and overtaking maneuvers up close, comparable to the atmosphere in a football stadium.

The pack raced towards the bend in the Affenzahn, the drivers briefly took off the gas, tilted the machine in a lean position and balanced it on the left foot in a breathtaking drift through the bends. Visually and acoustically, the performances were a pleasure for the battle strollers. This is exactly how four-stroke engines have to roar with open megaphones. Anyone who wanted to be successful could hardly avoid a Harley-Davidson. Harley engineers developed the XR 750 for the flat track. Thanks to the enormous pulling power of the V2, the good engine braking effect and the flawless chassis, the Milwaukee racer was named "King of the Track".

In August 1975, Yamaha factory rider Kenny Roberts shocked American flat track competition. In Indianapolis he pushed a machine to the start, in whose filigree chassis the 120 hp four-cylinder two-stroke racing engine of the Yamaha TZ 750 sat. In the final it came as it had to. In the last few meters, the young daredevil overtook Harley factory riders Corky Keener and Jay Springsteen with their XR 750 and won the race. That broke the barrel. The AMA immediately changed the regulations. From 1976 onwards, only machines with a maximum of two cylinders were allowed to start. Insiders were sure that it was Harley-Davidson himself.

The exceptional Kenny Roberts was far from the first to cause a stir with a two-stroke against the overpowering armada of Harley-Davidson. But his spectacular appearance and the consequences it caused were a topic of conversation in the scene for a long time and remained firmly in the minds of the fans. The years 1974 and 1975 are almost forgotten, when Erv Kanemoto’s racing team with Gary Nixon, Don Castro and Scott Brelsford on a Kawasaki 750 H2R came up with the idea of ​​the flat tracker with a road racing engine.

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In 1975 Scott Brelsford started with the Kawasaki Dirt Tracker in the AMA championship.

The highly talented technician and tuner with Japanese roots had been associated with Kawasaki-USA since the late 1960s. As a mechanic on the racing team, he looked after Gary Nixon’s Kawasaki 750 H2R road racing machine in 1973. At that time he was one of the most successful and popular athletes in the USA. With triumph he became AMA Grand National Champion and Daytona 200 winner in 1967 and 1968. In the 1970s he relied on Kawasaki and Suzuki. For the 1974 season, the full professional in the fight for the National Championship should also start in the flat track on Kawasaki. However, there was no question of a real factory machine. But on the contrary. The 750 H2R flat trackers were developed as a low budget racer on the initiative of Erv Kanemoto, who had meanwhile founded his own racing team. The team boss had the chassis built by frame specialist Champion in California according to his own specifications. For the 750 three-cylinder Erv Kanemoto only had to reach for the shelf.

By pulling a lever on the left end of the handlebar, decompression valves in the cylinder covers opened and the 7: 1 compressed engine was easier to push. A pump supplied the crankshaft with lubricant directly from the oil tank, while the piston and cylinder were lubricated by the 1:30 gasoline-oil mixture. The undamped H2R racing exhaust system nestled tightly against the frame on the right-hand side, as the flat track oval basically drives counterclockwise. A brake in the front wheel is forbidden, a disc brake at the rear served as an emergency stop. For this reason, the shift lever and brake pedal are located on the right-hand side. Erv Kanemoto consistently relied on weight reduction, the result of 120 kilograms was impressive.

Kawasaki 750 H2R dirt trackers (part 2)

12th Pictures

Pictures: The two-stroke experiment

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The course had been set for 1975. Team principal Kanemoto hired Don Castro and Scott Brelsford, the brother of Mark Brelsford, the 1972 Grand National Champion, and commissioned two more landing gears from Champion. However, the top favorite in the hard-fought championship was Yamaha works rider Kenny Roberts. The all-round genius had won the AMA Grand National Championship in 1973 when he was only 22 years old with a Yamaha XS 650 flat tracker drilled to 750 cm³, and in 1974 he repeated the trick. With the Twin, Kenny Roberts was inferior to the competition on the Harley-Davidson XR 750 in terms of performance. Thanks to his exceptional driving skills alone, he managed to get among the frontrunners. Kenny Roberts and Yamaha wanted to win the 1975 title again at any cost.

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Kawasaki 750 two-stroke triple against Harley-Davidson’s XR 750 four-stroke V2.

Erv Kanemoto’s two drift acrobats showed that the answer could be a two-stroke. This is how the Yamaha TZ 750 dirt tracker was born. The intermezzo of the 750 two-stroke flat track was flashy, but only short-lived. After Kawasaki had withdrawn from US racing in 1976 and Gary Nixon had become vice world champion in the Formula 750 with the Kawasaki KR 750, Erv Kanemoto hired Honda. He discovered and promoted Freddie Spencer, who promptly became the youngest 500cc world champion in 1983.

After the two-stroke engine ended, the 750-series Kawasaki flat trackers disappeared from the scene and threatened to be forgotten for good. “In the summer of 2004, an insider showed me pictures of a Kawasaki flat tracker in a private museum in the USA. Spontaneously I remembered the story and asked the owner if I could buy the bike, ”reveals Jurgen Weiss. The qualified engineer, who works in engine development, is a proven Kawasaki two-stroke expert and known in the scene as an H2 guru. Its collection includes all 750 H2 models as well as special H2 with special chassis and houses the largest collection of original H2R / KR 750 factory machines in Europe.

Soon the rarity was in his garage. “The technical condition was not great. I completely overhauled the tracker and set it up in the same way as Scott Brelsford started with the number 19 in the 1975 season. Unfortunately, there is hardly a possibility for us to show the largely unknown track racer in action to an interested audience. In return, the extraordinary machine is admired all the more at club meetings and exhibitions, ”says Jurgen Weiss with a certain pride in his tracker exhibit.

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