Half a century OF HAZE

Suzuki’s GT750 two-stroke triple was the factory’s first real superbike. John Nutting details its origins and rides two examples of a machine with a faithful following.

With 50 years having passed since Suzuki’s two-stroke GT750 was launched, it’s easy for many motorcycle fans these days to regard the bike as a bit of a dinosaur, a smoking throwback from an era of unbridled and eventually doomed excess. But at the time, we could hardly believe what we saw in the papers after the T750R, as it was then known, was unveiled at the 17th Tokyo Show in October 1970. In the 1960s, Japanese two-strokes meant performance, but largecapacity two-strokes were just a dream.

Kawasaki was first to translate that into reality with its Mach III in 1969. Despite being 500cc, the Mach III’s almost unbelievable acceleration was more than a match for Honda’s CB750 four, BSA-Triumph’s 750cc triple and Norton’s Commando twin, all fourstrokes. Surely then the Suzuki T750R, the first liquid-cooled superbike, would be even more phenomenal.

Top of the range from the Hamamatsu factory had until then been the 500cc Cobra, a bigger version of its air-cooled twins. With an extra cylinder, the T750R offered much more, with speculation that 75bhp would be possible, offering a top speed of more than 125mph. Few technical details were available, and Suzuki wasn’t even confirming that the bike would go into production.

Development continued and later in 1970 Suzuki invited dealers to see it first hand in the US and Europe. After appearing in Germany, the first bike in the UK arrived on Christmas Day 1970 in readiness for January’s Olympia Motorcycle Show. Even then the bike didn’t go on sale outside of Japan in 1971.

More improvements were made and the first opportunity for journalists to ride the machine, now called the GT750, was in California at the end of the year.

The GT750 was a Grand Tourer – as its title suggested – with smooth flexibility and a modest top speed in the region of 110mph, not a Kawasaki beater. So what was Suzuki’s management thinking when they conceived the bike?

Ray Battersby, who worked at Suzuki GB in the 1970s and is author of the definitive book about the factory’s racing machines, used his contacts to find out how the bike evolved. Suzuki’s president Jitsujirou Suzuki had called for the ‘ultimate two-stroke big bike’ to compete with Honda’s CB750 four, even if it was thought that anything larger than 500cc was impractical.

However, general manager Masanao Shimizu was confident that by employing liquid-cooling, which had been used on the racers, a 750cc two-stroke could be developed. Requirements for the GT750 were that the peak power should be 67bhp, the same as the CB750, with a flat torque curve and top speed of 180kph (112mph) and a low-frequency exhaust note, because people didn’t like screeching two-strokes. The bike should have low mechanical noise, especially the transmission, offer durability, and have high-speed stability for US freeways.

Engine design was the responsibility of Seiichi Suzuki (no relation to the company president), who had been familiar with liquid-cooling, but he realised that there were new challenges with a three-cylinder machine. The first was reducing the width across the cylinders. This was reduced by rotating the transfer ports so they overlapped.

The width across the gearbox was also reduced by taking the primary drive from between the two righthand cylinders. As a safety move, much of the coolant piping was included with the engine castings, but Shimizu faced leakage problems that were eventually overcome.

Shimizu was succeeded as race manager by colleague Etsuo Yokouchi, who was involved with the GT750 project after its launch to improve the bike’s performance and handling to satisfy riders in Europe. Yokouchi visited Europe in the autumn of 1973 to hear what the dealers and distributors had to say about the GT750. “Most GT750 buyers wanted more power and a better lean angle; the exhaust and centre stand were scraping the Tarmac too soon. Back in Japan he made the changes that were introduced on the GT750L in August 1974,” said Battersby. Yokouchi went on to take charge of testing the GS four-strokes in Europe and developing the GSX-R series.

Maurice Knight, who was sales director at Suzuki GB when the GT750 was launched, recalls that development had already been almost completed when he first saw the bike at the Hamamatsu factory in 1970. “When we took over the importing of Suzukis (by Lambretta-Trojan from Associated Motorcycles in 1969) there was already a range of machines up to 500cc,” he said. “The GT750 was a new item and we had nothing to do with what it would look like.”

Knight was invited to Japan with Suzuki GB managing director Peter Agg to see the new superbike. “It was presented to us as a package at the test track. And although we didn’t have any riding kit, they insisted we have a go. We had to borrow leathers and helmets, but they came from Japanese riders who were smaller than us. I was very uncomfortable, but went through the motions. We said we liked it and that we could sell it.”

But if the GT750 was well established as a gentlemanly highspeed tourer when the first bikes reached dealers in the UK, the faint hope that it could be a fire-breathing monster was fuelled by the news that the factory in Japan had been working on a racing version.

With the objective of winning the following year’s Daytona 200 race, and the US national series, Suzuki had produced bikes with special engines churning out 107bhp at 8000rpm, a phenomenal figure at the time. In practice for the race, the TR750s were the fastest ever fielded, topping 170mph on the Florida bowl.

Simply sophisticated

Once the GT750 had arrived, more about its technicalities was revealed. The crankshaft was like previous Suzukis, being pressed-up with four large roller bearings, but at 120-degree intervals, and with the primary drive by helical gear between the middle and right-hand pots.

Overlapping the transfer ports reduced the overall width to 71cm. Like the T500 Cobra twin, bore and stroke were 70 x 64mm, giving a capacity of 738.9cc. From exhaustport closure the compression ratio was a modest 6.7 to 1. Steel liners with simple porting – an oval exhaust, two transfers and an inlet – were cast into the aluminium-alloy block which was topped by a cylinder head casting secured with 11 studs.

Liquid-cooling meant that the engine’s temperature could be maintained at the optimum 80degC. Coolant was circulated at up to 20 gallons a minute by a vane pump in the bottom of the cases. To speed warm-up the thermostat on the cylinder head recirculated coolant until the correct temperature was reached when the large radiator came into play. On the original models it was thought necessary to include a fan, but even under the hottest conditions it was redundant.

The more consistent temperature meant that cylinder-to-piston clearances could be reduced to 0.0019in, compared with the aircooled Cobra’s 0.0028in, reducing power losses and mechanical noise. Breathing through three 32mm Mikuni carburettors, and exhausting through four silencers (the middle pipe being bifurcated, though connected with cross pipes at the headers), peak power at 6500rpm was claimed to be 67bhp, the same as Honda’s CB750 four-stroke four.

Lubrication for the cylinders and main bearings followed the then common two-stroke practice of feeding oil from a tank in a total loss system, but with more refinement. Oil was fed with a pump mounted on the top of the gearbox, and its delivery to the main bearings (and thence to the cylinders) was controlled by engine speed and twist grip action. To minimise oil collecting in the crank chambers, feed pipes connected the chambers to the adjacent transfer ports with one-way valves.

Electrically, Suzuki used a generous 280-watt alternator on the right side of the crank, while on the left was the starter motor behind the cylinders driving through gears and a one-way clutch. Outboard of this the ignition’s three contact breakers were operated from a cam with its own shaft keyed to the end of the crank. To minimise vibration transmitted to the rider, the engine’s frame mounts used rubber cushions. As first offered, the GT750 was large and luxurious with a smooth and flexible power delivery.

With three flavours of candy and white paintwork augmented by acres of polished alloy and chrome, its styling was more ice-cream parlour than the gran turismo its name suggested.

When the first GT750J model was tested by the weekly paper Motor Cycle at the MIRA proving ground in March 1972, conditions weren’t at their best, with a damp surface and a strong three-quarter wind blowing across the timing straight (see boxout for performance figures), but the big disappointment were the brakes.

Despite the front brake’s potent appearance, with a double-sided 220mm drum and twin-leading shoes, stopping power was unimpressive. To its credit, the factory responded to criticism of the brakes.

Before the following year’s 1973 model was introduced, a conversion kit was offered with dual hydraulic discs, and this appeared on the GT750K, along with detail alterations including chrome radiator covers, flexible mounts for the carburettors and finned exhaust clamps.

For the GT750L in 1974, the carburettors were changed, this time to CV types – along with a new air box and slimmer side panels – with a smoother action. Styling changes included a chromed headlamp shell and dropping of the fork gaiters. A digital gear indicator, along with the warning lamps, were mounted between the clocks.

Despite the sportier looks, performance was unchanged.

By now, other manufacturers’ new bikes – Kawasaki had launched both the 750cc H2 and the 903cc Z1 four-stroke four – were showing up the Suzuki’s modest performance. Suzuki was in the final stages of launching its rotary-engined RE5 for 1975 and pursuing the development of its first modern four-stroke, the GS750 four. It needed to inject a new lease of life into the GT750.

That was provided with a power boost and styling update for the 1975 GT750M. Along with a number of styling changes included earlier, such as dual front discs, the M’s engine was revised by raising the inlet ports by 5mm and the exhaust ports by 2.5mm, and shaving the cylinder head face by 0.2mm to increase the compression ratio.

This, along with a redesigned exhaust system offering better cornering clearance and larger 40mm-choke CV carbs, raised the peak power to a claimed 70bhp, although at the expense of the lowend punch of the earlier models.

It was humid and hot in August 1975 when I took the GT750M to MIRA’s timing straight for the performance testing. We were amazed when the bike became the fastest 750cc roadster of its day, based on the MIRA figures. Overall gearing had been raised by 16% with final-drive ratio of 43/16 to give almost 120mph at 6500rpm, and this turned out to be almost spot on.

Acceleration was also much better, with the standing quarter-mile time cut to 13.5 seconds with a terminal speed of 99.5mph. Braking for the slightly heavier version was also better with the discs, with a stopping distance of 30.5ft (9.3m). During my road test of the machine I’d expected heavier fuel consumption due to the higher state of tune, but overall it averaged 45.3mpg; no worse than other superbikes of the day.

For its final model year in 1977, the GT750’s styling was harmonised with Suzuki’s newly launched GS750 four-stroke four that would carry the factory’s torch into an era of increasingly tough exhaust emissions in which banned the sale of big two-strokes.

Riding the kettles

One thing is sure when you ride Suzuki GT750 triples: you get attention. These two kettles owned by owners’ club chairman Dave Hewitson date from the early and late periods of production. The gorgeous gold GT750K is a 1973 model, identified by the original styling of the side panels, asymmetric headlamp shell, conventional Mikuni carburettors, connectors between the exhaust pipes with their black tail pipes, but with the dual disc brakes, which replaced the 1972 launch model’s double-sided 2LS drum.

The blue GT750A was first registered in late 1975 and features less radical styling, with the more highly tuned engine using a revised exhaust system and bigger CV carbs. Since 2003 it has been a workhorse touring machine for Dave, having been used on five trips to the continent loaded with a passenger and camping gear, which is why it has been fitted with more comprehensive crash bars and luggage carrier.

I’d ridden examples of Suzuki’s liquid-cooled two-stroke triple many times before, and not with pleasant memories of some, so I approached Dave’s bikes with a slightly jaundiced view of their capabilities.

But I’d barely swung a leg over the special K before I felt relaxed and at home. It’s all original, apart from the addition of engine protectors and the carrier, having been subject to a detailed nut-and-bolt resto that included replacement bodywork. You sit in the bike and grip a broad medium-height handlebar that provides ample leverage.

Switch on between the instruments, apply a smidgeon of mixture and press the twist grip button to bring the motor to life with its signature pokkety-pokkety exhaust note. Mounted in rubber supports, the engine dances about at idle, but once on the move it smooths out well.

Unlike on a Kawasaki triple, the Suzuki’s cooling jacket subdues much of the mechanical racket, but the nasal drone from the combined effects of the air-box and exhaust are unmistakable.

Once out on the roads of rural Buckinghamshire, the characteristic blue haze of the burnt oil from the pipes cleared and I slipped into the Suzuki’s unhurried rhythm.

Typically there’s a note of hesitancy in the response at small openings, especially if the revs are high as you snick down the five ratios, but the K liked its lower revs being used as you wound up through the neverending bends that cut through the agricultural landscape.

Gearing had been raised by Dave with a one-tooth bigger engine sprocket, while for reliability the ignition is a fit-and-forget Accent digital system.

I was also surprised that the throttle action was so light: the grip’s single cable is connected to three, one for each carburettor, and a fourth for controlling the oil pump.

Handling is soft and cushy, the steering light, and the suspension compliant, just what you’d want for covering high mileages. Dave says he’s got up to 55mpg from the K, a surprise for a big two-stroke.

The GT750A proved to be a harderedged machine, mainly I think because the Progressive fork springs and Hagon rear shocks were stiffer.

As on the K, tyres were Bridgestone Battlax in the standard sizes, and matched the handling well, offering easy-going bend-swinging but without the soft touch that I liked about the earlier bike. Certainly, the higher strung tuning of the A that I loved back in the seventies doesn’t seem so appropriate now.

For bikes well into their 40s, both of these GT750 triples were wellprepped examples in their prime.

According to Dave, owners don’t get pedantic about this or that engine or chassis number, they just get out there and ride them.

After all, it’s not about the money. It’s all about keeping the blue haze flowing.

“For bikes well into their 40s, both of these GT750 triples were well-prepped examples in their prime. According to Dave, owners don’t get pedantic about this or that engine or chassis number, they just get out there ...”