‘IT’S UNLIKELY THE GL750 EVER RAN WITH INJECTION... BUT IT’S STILL YAMAHA’S SECRET’
The biggest disadvantage would likely have come from tiny air leaks from perishable rubber hoses, faulty connections or the pump. The resultant performance drop could easily be detected on a single-cylinder engine, however a person riding a multi-cylinder two-stroke may have opened the throttle more to compensate, which would have culminated in a hot cylinder followed by seizure.
Interestingly, no cables were visible connected to the uncluttered injection system – so it’s unlikely the GL750 ever ran with fuel injection fitted, although over four decades later Yamaha still wishes to keep its operation secret! However, Mick Andrews took his works Yamaha OW10 to victory at the French round (Sancerre) of the 1974 European trials championship using the company’s crankcase pressure-induced fuel-injection system on the low-revving motor.
The double-cradle chassis had a 1450mm wheelbase exclusive to the lightweight (205kg) GL750. The frame and running gear also bristled with innovation, such as twin XS2 front disc brakes with Nissin calipers and master cylinder, Takasago alloy race wheel rims, Showa forks and shocks, DID 530 chain and Dunlop tyres. Looking closely, the 17-litre slimline fuel tank appears to be a cut-down TX750 tank (not built for another year). It’s likely the GL750 was to have been the genesis for future model spin-offs, although Yamaha waited until 1980 before it built its next water-cooled road bike, the RD250/350LC, or fitted an alternator behind the crank – as on the XJ650.
At first glance, the distinctive white seat is probably the most recognisable feature – likely to be the only motorcycle Yamaha ever made with a seat in that colour!
After only six months of secret development, the mock-up GL750 was ready for the 1971 Tokyo Motor Show, staged that year from October 29 to November 11, where it shocked the motorcycle world.
There’s also proof that Yamaha was still perfecting the GL750 in early 1972. During a visit to Yamaha Japan by Ludy Beumer, a Yamaha Amsterdam employee (and classicyams.com founder), he saw a GL750 running at the Fukuroi race track – this time using Mikuni carburettors in place of the fuel injection.
“They were just casually running it around and maybe doing 60mph, but no faster. One or two laps and then they disappeared again in a shed,” Beumer recalls.