rubber_side_down: A local legend's wild ride

The recent Cycle World International Motorcycle Show in San Mateo included an intriguing racing relic with local significance.
Amid a display of flat track racers, including an example of the dominant XR750 Harley-Davidsons, was a homely, cobbled together yellow motorcycle that looked nothing like the other flat trackers.
It looked like something a mad scientist or someone with a very perverse sense of humor would conceive: it had a flat tracker chassis and running gear, but stuffed in the engine bay was a four-cylinder, two-stroke Yamaha road racing engine.
This was the bike that Stanislaus County native and racing legend Kenny Roberts Sr. used to win the Indianapolis mile in 1975 – a win that was highly improbable and demonstrated Roberts’ prodigious talent on anything with two wheels.
Some background: Harley-Davidson has long dominated flat track dirt racing, done on dirt ovals of various sizes. The mile is the hairiest of them, with racers pitching their bikes sideways, handlebar to handlebar, at 90 miles per hour as they slide around the corners with one steel-shoed foot on the ground for balance.
The Harleys are particularly well-suited to the dirt ovals because they have a broad, flat power band, and don’t develop too much horsepower, which would overwhelm the traction available.
Harley factory riders typically top the standings in the dirt oval racing. Roberts, however, was a Yamaha factory rider. Yamaha at the time was dominant in road racing, due in large part to Roberts, but its parallel twin, four-stroke XS750 flat tracker wasn’t very competitive against the Harleys.
So someone had the idea to take the Yamaha TZ750 two-stroke road racing engine and stuff it in a flat tracker.
The logic behind it is hard to fathom. The road racing engine’s characteristics seemed the opposite of what had been proven to work. The TZ750 had a very narrow powerband, developing huge horsepower high up in the rpm range.
That worked on dry pavement, where horsepower and top speed were important, but on dirt with limited traction, a sudden, violent power burst at high revs seemed like a recipe for disaster.
Roberts started at the back of the pack, and wrestled the machine through the field, making the final pass for the win on the last lap.
He famously remarked afterward, “They don’t pay me enough to ride that thing.”
It was nice to see “that thing” in person, after having read so much about it.