All-conquering King Kenny takes on the Harleys - and wins

By mid-1975, a fresh-faced 23-year-old with short hair and a neat side parting knew his chances of retaining the US Grand National Championship were slipping fast.

• The sport: Motorcycling
  The event: Indy Mile
  The place: Indiana State Fairgrounds
  The date: August 23, 1975

Back then Ken Roberts was a two-time GN title winner and the clean-cut corporate image for burgeoning Yamaha brand in the United States.

Only much later would the super talent from Modesto, California, become Kenny, and on winning three world championships, King Kenny.

The unique format of the Grand National series meant riders had to compete in five disciplines - road racing, short track, TT, half-mile and mile, the latter four on dirt ovals.

Roberts had the road racing side nailed, the newly introduced TZ750 four-cylinder two-stroke Yamaha was all-conquering.

While he was holding his own in the shorter dirt events, his ageing twin-cylinder four stroke Yamaha was down on power compared with the XR750 Harley-Davidsons in the prestigious mile races.

Mentor and former world champion Kel Carruthers had the answer; slip a TZ750 engine into a dirt track frame.

He created a monster.

Some said it was unrideable.

And even Carruthers must have had doubted whether his protege was up to even keeping it pointed in the right direction.

The engine spat out 125hp, 50 more than a Yamaha twin, and the bike was capable of reaching 240kmh - in less than 500m on hard-packed dirt.

Oh, and to slow it, Roberts would have to throw the bike sideways into a cushion of loose dirt.

As Roberts drily remembered: "There weren't a lot of riders who could throw it sideways at 240kmh."

The bumblebee yellow and black machine made its debut at the Indy Mile, at the Indiana State Fairgrounds, Indianapolis, in August 1975.

Not that I even knew about it.

Remember, this took place in the years before the internet and cellphones, and faxes, even; a time before press releases and media hype, when newspapers were printed in black and white.

It was probably nearer December 1975 when the sea-freighted glossy US magazines hit bookstands around the world describing Roberts' feat.

Oh, to have been there, to hear the raucous crackling and popping of the unsilenced Oriental demon warming up, then its glorious piercing wail in full flight.

All this, assaulting the ears of Harley-worshipping heartland America.

Remarkably, mere seconds of flickering footage in the 1980 movie Take it to the limit are the only moving images of the event.

Somehow Roberts qualified for the 25-lap final, achieving a delicate balance of throttle and traction control.

"In the main," Roberts recalled years later, "the cushion went right up to the hay bales.

"After the race, I had baling wire on the bike from bouncing off the bales."

Fighting for control every lap, Roberts somehow closed on the leaders, the "Michigan Mafia", Harley riders Jay Springsteen, Corky Keener and Rex Beauchamp.

Then, on the last lap, "I got a terrific drive off turn three.

"I have no idea why.

"The tyre was almost gone, three-quarters chunked.

"Coming off the last corner, I definitely had third, and I thought I could get second.

"I hit fifth gear and it was less than a quarter mile at 145[mph], so everything happened quickly."

Roberts blew past the Harley trio for the win.

But it was to be the bike's sole, spectacular moment of glory.

The sport's lawmakers banned it within months, perhaps on reading Roberts' thoughts.

"They don't pay me enough to ride that thing," he said.

• They still weren't paying Roberts enough, he claimed last August, when he remounted the bike for the first time in 34 years and put in some demonstration laps at the same venue.

And in this age of the internet, images and sound abound, including one memorable moment.

"What was that?" an excited female voice drawls as King Kenny howls past, hugging the fence, spraying loose dirt over his adoring, cheering subjects.