Supercharged! The Yamaha SR400 gets Kruggered

World champion bike builder Fred ‘Krugger’ Bertrand turns his hand to the Yamaha SR400, and the result is incredible.
We’re not sure how much longer Yamaha can keep the iconic SR400 on its roster. With European emissions laws tightening, its days are numbered.

Still, the plucky little thumper remains a favorite with custom builders—even superstars like Belgium’s Fred ‘Krugger’ Bertrand, who has won the AMD World Championship twice.

World champion bike builder Fred ‘Krugger’ Bertrand turns his hand to the Yamaha SR400, and the result is incredible.
When Fred was asked by Yamaha Motor Europe to build a bike, any bike, the SR400 was his top pick.

And why is that, when acclaimed modern Yamahas such as the XSR700 are available? “Because it’s a light machine with a single cylinder,” says Krugger simply. “A return to the basics of a bike.”

World champion bike builder Fred ‘Krugger’ Bertrand turns his hand to the Yamaha SR400, and the result is incredible.
The brief was wide open, so Krugger decided to build a compact cafe racer: a supercharged tribute to another very skilled Belgian bike builder, the MotoGP mechanic Bernard Ansiau.

Bernard (below, right) currently swings the spanners on Valentino Rossi’s Yamaha—and has worked with greats like Wayne Rainey, Kenny Roberts and Mick Doohan.

Belgian world champion bike builder Fred 'Krugger' Bertrand and famed MotoGP mechanic Bernard Ansiau.
“I admire his work,” says Krugger. “I’ve worked a lot in motorsport, and the job done by mechanics in the shadows is part of the victory of the pilot. But they are rarely mentioned. Here, I am contributing in my own way.”

“In agreement with Bernard, I went into the aesthetics and racing spirit of the 70s—a tribute to the famous Yamaha TZ line and quite faithful to Bernard’s career.”

World champion bike builder Fred ‘Krugger’ Bertrand turns his hand to the Yamaha SR400, and the result is incredible.
The SR400 now looks far more racy than when it rolled off the assembly line. And there’s a helluva lot going on under the hood: Notably a tiny Aisin 300 supercharger—also used by Subaru for its smaller Japanese market cars—along with a custom plenum chamber and a belt-drive setup for the compressor.

World champion bike builder Fred ‘Krugger’ Bertrand turns his hand to the Yamaha SR400, and the result is incredible.
The SR400’s fuel injection is gone too, replaced by a 48mm carb from S&S Cycles and a hand-made intake. (It’s designed to run with either an open velocity stack or a filter.) And the stainless steel exhaust system is a one-off.

World champion bike builder Fred ‘Krugger’ Bertrand turns his hand to the Yamaha SR400, and the result is incredible.
The tank is stock, but it’s been narrowed and stretched. Krugger has also reworked the frame—cleaning up the welds, modifying the junction with the steering neck, and reconfiguring the rear loop at a steep angle.

World champion bike builder Fred ‘Krugger’ Bertrand turns his hand to the Yamaha SR400, and the result is incredible.
A custom tailpiece houses the electrical components, and there’s a small cowl up front to cap things off.

The forks have been lowered and polished, and there’s a new set of Fox shocks holding up the rear.

World champion bike builder Fred ‘Krugger’ Bertrand turns his hand to the Yamaha SR400, and the result is incredible.
Krugger’s tires of choice for this build are Dunlop K81s, based on the pattern of the first tire to lap the Isle of Man TT course at over 100 mph.

The looks remain the same as the 1969 original, but the rubber compound has been brought up to date.