WES COOLEY’S YOSHIMURA SUPERBIKE
In 1979, Wes Cooley finished on the podium at every round of the US AMA Superbike Championship on his Yoshimura GS1000 to claim the title. It was the start of something big, putting Yoshimura on the map and – though it would only last a few seasons – spearheaded an exciting era of Superbike racing in the USA.
Cooley was already an experienced racer by the time he hooked up with then-emerging tuner Hideo ‘Pops’ Yoshimura in 1976 – the first year of AMA Superbike racing. Yoshimura was campaigning Kawasakis then, but he switched to Suzuki during 1978. It was the right call, and in 1979 Wes Cooley and Mike Baldwin won the prestigious Suzuka Eight-hour race in Japan. After that, Cooley went on to take the AMA Superbike crown on the Yoshimura Suzuki GS1000.
Amazingly, the frame was largely stock Suzuki, though gusseted to make it a little bit stiffer. Yoshimura had forged excellent links with Suzuki – through these they were supplied with Kayaba forks and shocks, and the team used American-made Harry Hunt alloy discs.
Engine-wise, Pops and the boys knew pretty much what they were doing – partly because of their experience with the Kawasaki engine. Suzuki’s GS750 and 1000 engines owe a lot to the Z1. They’d developed two-ring pistons that had lasted the previous year’s Suzuka Eight-hour race and Pops was the master at hand-grinding performance cams and porting cylinder heads. There was a steel roller in place of the slipper to control the camchain at the top of its run, plus beefed-up clutch damper springs. The valve springs were largerdiameter with Yoshi’s own guides and the clearances were set by Yoshimura’s own shim-under-bucket arrangement.
All of that was good for around 130bhp – a huge output for a modified road engine back in 1979. It was enough to win big for Wes Cooley – but also enough to push the modified rolling chassis to the limit – especially when running slick tyres.
Cooley proved himself the man to tame the beast, though, and followed up his 1979 series win with another series victory in 1980. But he couldn’t have done it without Pops. Sometimes it takes two to tango.