Yamaha’s iconic SR400, first introduced in 1978, had its production potentially discontinued again in 2021, but it remains a hot favorite among Japanese custom builders. Upon unveiling the mannequin, Yamaha designer Atsushi Ishiyama acknowledged that the XS650 had a profound impact on the design. The SR’s design was heavily influenced by iconic British motorcycles from the 1960s, thereby inheriting timeless and traditionally styled aesthetics. The bike’s single-cylinder 400cc engine also conformed to the less stringent Japanese Domestic Market (JDM) regulations for smaller capacity motorcycles, making it more affordable and compliant with local laws. The combination of these innovative features and a competitive price point made the SR400 an attractive option for Japan’s younger population. As a result, Yamaha continued to produce the SR model in large quantities, and its enduring popularity led to it remaining in production for over four decades.
In Japan, a trend among young people emerged for customising their vehicles with SR patterns, but it didn’t take long for aftermarket manufacturers to capitalise on this craze. Across the country, numerous workshops specialize in customizing SR components. Located approximately 40 minutes east of central Yokohama lies the Sweet Bike Laboratory, a two-man workshop.
With a focus on all matters pertaining to the iconic Yamaha SR series, Sweet MC Lab excels in providing comprehensive services ranging from routine maintenance to bespoke, from-the-ground-up customizations. A cursory glance at their portfolio reveals a versatility that knows no bounds, suggesting they’re equally adept at handling any project or concept, regardless of its SR designation.
Sweet MC Lab’s customers sought the ultimate SR cafe racer: a sleek, agile neo-retro motorcycle packed with performance-enhancing features and boasting a striking design that turns heads in droves.
Particular attention was devoted to the meticulous handling of all SR-related matters. Notably, engineers familiar with SR400 design will discern a drastically reconfigured rear-end configuration on this motorcycle. The Sweet MC Lab design deviates from the conventional twin-shock setup by incorporating a single-sided Professional Arm swingarm, paired with a monoshock sourced from a late-model Ducati Hypermotard. The adjustments have been made possible through the creation of a novel subframe, which has significantly reduced the bike’s dimensions. The revised rear-end suspension has been further enhanced by swapping out the existing entrance finish for Showa USD forks, contributing to an enriched overall riding experience. The installation of the forks required the design and construction of a novel prime clamp, which now accommodates a miniature Motogadget digital speedometer.
With its single-sided swingarm design, the SR400 sports a specially fitted rear wheel, tailored to its unique specifications. To maintain the bike’s classic visual appeal, Sweet MC Labs specified a Borrani spoked wheel, carefully paired with a bespoke hub to create a unique and striking design element. The incorporation of the Ducati rear finish has resulted in enhanced braking performance thanks to the Hypermotard’s disc brakes. Sweet MC Labs has further elevated its stopping power by replacing the 298mm front disc with a larger, 320mm unit paired with a Brembo caliper and master cylinder for enhanced braking performance.
Sweet MC Labs has entrusted its in-house manufacturing facility to craft the ultimate finishing touches for their final SR cafe racer design. A unique fuel tank substitute is discovered, originally from a BMW R100, which has undergone customization to feature a slimmed profile and a sleek alloy Monza-style filler cap, adorned with distinctive Sweet MC Labs roundels. The sleek, diminutive tank nestles comfortably on the sturdy rails of the SR chassis, while at its rear, it meets a luxurious suede-upholstered single seat, beautifully finished with classic diamond stitching.
With the engine now respirated by a velocity stack, the airbox and facer covers are no longer needed. By concealing unsightly electrical components, Sweet MC Labs has developed an innovative outdoor aluminum battery enclosure, seamlessly integrating aesthetics and functionality. All manufacturing facility lighting has been replaced with energy-efficient LED options to further reduce the facility’s operational burden. The headlights feature a modern projector-style LED design within a conventional bucket, while the taillight takes the form of a sleek strip integrated seamlessly into the rear spoiler. The Flip Alerts feature discreet Motogadget Mo.Blaze pins seamlessly integrated into the bar ends and subframe.
Without a doubt, no cafe racer endeavor would be complete without a range of engine enhancements; and this SR model is no exception, boasting an impressive array of modifications. At the pinnacle of the lineup stands an impressive 534cc output, courtesy of a novel prime-finish cylinder head and 90mm high-efficiency pistons. Internally, we also have an inventory Yamaha SR500 crankshaft and ST-1 cams in place. The FCR 41mm carburetor provides a fuel supply for the demanding single-cylinder engine, while emissions are managed through a bespoke stainless steel exhaust system featuring an underslung muffler designed to keep noise levels within acceptable parameters.
The end result showcases the remarkable versatility of Yamaha’s iconic thumper, highlighting its capabilities in an impressive motorbike design. The decline of a once-beloved product is indeed a crying shame; their discontinuation has left a gaping hole in the market.
