During the early 1970s, Kenny Roberts shot to stardom as a rider in the American Yamaha racing team. In 1973 he knocked the top dog of the dirt track, the Harley Davidson XR-750, off its perch riding a seemingly outgunned Yamaha XS650. When his racing moved to sealed surfaces he piloted his legendary Yamaha TZ750 to countless victories in both the United States and around the world. Such was his influence in the world of motorcycle racing that King Kenny’s race bikes have been replicated by devoted fans time and time again. This particular Kenny Roberts inspired bike hails from the far eastern reaches of Japan. Koga City to be precise. Which is where you’ll find Yutaka Hoshi and his workshop Rocket Motorcycle.
Hoshi-san has been building custom motorcycles as a one-man operation since 2004. Along with preparing bikes for customers, he’s an avid fan of racing both on and off the dirt, much like the King himself. So late last year, after the announcement of the 2020 ‘Legend of Classic’ historic motorcycles races at Fuji Speedway, Hoshi-san decided to build himself a new race bike that oozed Kenny Roberts cool.
Hoshi-san’s Kenny Roberts Yamaha takes a slightly different approach to most. Rather than building an exact replica, he opted to combine the engineering of the King’s flat track XS650 with the styling of his TZ750 track bike.
The idea was dreamt up after the donor for the project, a 1980 Yamaha XS650 Special, was acquired from a friend. The XS had been sitting neglected but Hoshi-san saw potential in the bike thanks to a recently rebuilt engine. To ensure it had enough grunt for the race track Hoshi-san kicked things off with a few performance upgrades. The parallel-twin now runs a 750cc top end and a high-performance cam. A pair of bell mouthed CR carbs deliver the go-fast juice while a custom 2-into-2 system vents the exhaust gases.
For the bodywork, Hoshi-san took a less is more approach with his homage to the King. He sourced a replica of the most icon element of Robert’s TZ750 – the front fairing. However, rather than completely enclosing the front end, he went with only the top half of the kit. This leaves the engine exposed to help keep engine temperatures in check out on the track. A svelte fiberglass tail was also added in the rear rather than the boxy item Kenny ran on his bike. As for the fuel tank, it’s an aluminum unit Hoshi-san built from scratch. Being the first alloy tank he’s ever built he admits this was the most challenging aspect of the build, but the result speaks for itself.
Since this XS650 is destined for the track there’s no need for lighting. This meant the wiring loom could be reduced to the bare minimum. For ease of use, it’s still running a battery and starter, but there’s very little else in the way of electrics. Beneath the windscreen, Hoshi-san installed a single tachometer mounted between a set of clip-on bars. A specially made battery tray and oil catch can live beneath the seat.
As for the handling, Hoshi-san has upgraded everything using period looking Öhlins alternatives. In the rear, there’s a pair of STX 36 Twin Shock Classics and the forks have been rebuilt using an Öhlins cartridge/spring kit. The wheels also received an upgrade by lacing alloy Excel rims to the XS hubs. Rear set footpegs set things up for more aggressive cornering and Dunlop TT 900 GP classic race rubber provides ample grip.
To tie things back to the motorcycles that inspired this project the bodywork wears classic Yamaha speed block livery. Rather than the obvious Yamaha yellow paint scheme, Hoshi-san has finished the bike using a brilliant gold. This is perhaps an indicator of his aspirations for the 2020 Legend of Classic races in March. One thing’s for sure. If this Yamaha XS650 goes anywhere near as good as it looks he may very well end up atop a podium.
Photo by Tsuyoshi