Cut off in its PRIME

Suzuki's GT750 two stroke triple might have gone on a greater success had it not been upstaged by four stroke development. John Nutting has ridden both the early and late versions of this iconic Japanese machine.

THE development of electronics wasn't fast enough to stop the road-going two stroke engine being outlawed in the Eighties. Had they been, we might now be riding sophisticated descendants of the Suzuki GT750 developing more than 150 bhp, using clever fuel-injection systems and lubrication operated by high-power computers.
As it is, the automotive industry had no option in the face of tightening exhaust emission laws during the Eighties than to take the easier option of phasing out two strokes for road bikes in favour of four strokes. For many fans of the two stroke, with its inherent simplicity and flexibility of application for both road and sport, it was a dark day when production of high performance road bikes ended in the late Eighties.
Two strokes live on of course in scooters, and many incorporate engine control systems, but the chance of a big two stroke machine returning is remote. Suzuki, like Yamaha, had built its reputation on sizzling two strokes evolved through the Sixties.
Its biggest coup was when it tempted racer Ernst Degner to defect from the East German MZ factory and join them - with the secrets of Walter Kaaden, its fabled engineer, who had raised the performance of its disc-valve two strokes way beyond anything the Japanese had been capable of. With a fist full of world road racing championships won during a period of increasing consumer wealth, Suzuki offered bigger and better bikes.
This followed its two stroke twin theme culminating with the T500 Titan in 1968. Like Yamaha, Suzuki was cautious in offering a 750 to follow Honda and Triumph's lead that same year. But when eventually it did, riders were stunned. The 750cc three was revealed at the 17th Tokyo Motor Show in October 1970.
With liquid cooling, four exhaust pipes, a 150 mph speedo and a 7000 rpm red line, the bike was a bombshell. Few details were available, but reports speculated that it could produce in excess of 70 bhp, offering a top speed of more than 120 mph. Having whetted riders' appetites, Suzuki kept the bike under wraps and continued development of what was originally called the T750R. This is according to The Kettle Club, the owners' club formed in 1995 to support the continuing use of the two stroke triple. The first GT750s appeared on the US west coast at the end of 1971 but first hopes of a two stroke rocketship like Kawasaki's Mach III would be dashed. It was a heavyweight luxury Grand Tourer - as its title suggested - with smooth flexibility and modest top speed in the region of 110 mph.

Lost in time
JUST why the GT750 turned out to be so gentlemanly is probably lost in the mists of time. Unlike today when project chiefs for superbikes are as much heroes as the racers who win on them, access to the designers was impossible. Indeed, few, if any, journalists before 1976 went to Japan to quiz the engineers.
Whoever it was, they did their best with a huge challenge of squeezing three cylinders across the bike, hanging a generator, electric-start drive and ignition system on either end and still making it only slightly wider than a CB750 Honda. The water jacket - a first on a two stroke roadster from Japan - helped, along with twisting of the transfer and exhaust port axes to save space. Tuning was softer than the T500 though it used the same 70 x 64mm (giving 738.9cc) bore and stroke dimensions. With 32mm VM Mikuni carburettors and a 6.7 to 1 compression ratio, the engine developed a claimed peak power of 67 bhp at 6500 rpm with maximum torque of 55.7 lb-ft at 5500 rpm. Although the prototypes boasted electronic sparks, coil ignition with three contact breakers were used on the production models.
As with most two strokes, the crankshaft was built up with ball main bearings and roller big ends lubricated by a pump whose output was controlled by engine speed and throttle opening. Power was delivered by gears between cylinders one and two (from the right) to a five-speed all-indirect gearbox and drive chain.
Top gear gave 110 mph. The design plot was lost with the chassis. A conventional duplex steel tube frame held everything together but up front a double-sided twin leading shoe drum provided the braking. Styling matched the bulk of the exhaust system in which the silencers for the two outer cylinders were complemented for the sake of symmetry with a bifurcated middle system. Ahead of the cylinders, a radiator with a cooling fan maintained the temperature at about 80 deg C. Styling was straight out of Thunderbirds, with swoopy lines for looks rather than function - and vivid turquoise paint.
Riders were impressed with the engine's smoothness, quietness and flexibility, admiring the way in which it would pull strongly from as 1500 rpm while offering relaxed cruising at above 80 mph. But there was a sting in the Suzuki's tail. Suspension that was inadequate for the GT750's tanked-up weight of 560 pounds, limited cornering clearance, poor braking and Bridgestone tyres that were frightening in the wet added up to a bike that called for respect when the road surface was suspect. Having joined the staff of Motor Cycle in April 1972 I was unlucky to have just missed testing the first version available on the UK market, the GT750J.
Still a bit wet behind the ears, I thought the Suzuki looked fantastic, and the idea that a Japanese factory would offer a high-performance motorcycle with such inadequacies seemed impossible. I soon found out the truth.

Safe distance
NEARLY two decades later, my rose-tinted goggles were cleared. For a magazine feature about the GT750 I rode a model restored by Lee Chambers, who at the time was offering his paint services professionally from his home near Wolverhampton. Looking for a suitable section of road to take riding shots I was following photographer Dave Goldman's car at what I thought was a safe distance. He pulled up sharply to avoid another car but the Suzuki's front brake gave up the ghost. Dave glanced in his rear view mirror to find it rapidly filling with GT750 and its rider mouthing profanities.
"I wondered why you were aiming for the gap next to the kerb," he said. Too right. Writing at the time I said: "The suspension lets the Suzuki down, especially this one. Displaying more than their fair share of stiction the front and rear shock only really work properly at speeds above 60 mph and offer a harsh ride and interference with the steering at town speeds. "You wouldn't be advised to use the Suzuki for hard riding on country roads, either back in its heyday, and less so now.
The stiff suspension, and exceptional weight, conspired to set up an incipient weave which would at high speeds expose itself at the slightest provocation. "And how on earth did we get along with such skinny 3.25 x 19 and 4.00 x 18 bias-ply tyres?" Metzelers had been fitted, but there was just too much bike for them to provide adequate stability. "To some extent, the lack of cornering clearance - even by early 1970s standards - is a mixed blessing." That wasn't all. The exhaust produced a smoke screen and the lights were poor. Even judged against its peers, the big Suzuki was a hairy beast.
To its credit the factory responded to the criticism. Before the following year's 1973 model was introduced a brake 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 again changed with CV types, a new air box and side panels. Fuel consumption, ranging from 43 to 48 mpg hadn't been a problem but the new carbs were lighter and smoother in action. Styling changes included a chromed headlamp shell and dropping of the fork gaiters.
A small gear indicator, along with the warning lamps, was mounted between the clocks. Despite the sportier look, performance was unchanged. By now, other manufacturers' new bikes were showing up the Suzuki's modest performance. Suzuki was in the final stages of launching its rotary-engined RE5 and completing the development of its first 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 1975. Longer timing, by raising the exhaust and transfer ports and lowering the inlet, along with a slight increase in the corrected compression ratio to 6.9 to 1 and the fitting of larger 40mm-choke CV Mikuni carbs, raised and narrowed the power curve at the expense of flexibility. Peak power was lifted by three bhp to 70 bhp at 6500 rpm. A figure for peak torque wasn't revealed. The styling changes brought the GT750 more in line with other models in the range with cleaner lines for the larger 3.75 gallon (17 litre) fuel tank and side panels.
One-piece exhaust pipes with revised baffling and better cornering clearance were adopted. The changes completely transformed the Suzuki and, although still bulky, provided a higher level of excitement. With a distinct leap in the power delivery at 4000 rpm, throttle response was better and acceleration improved through the gears, the ratios of which were raised to accommodate the extra power.

Time to start rebuilding the chassis - (Full engine rebuild later folks)

Yamaha RD500LC
THE parts have all been located for the engine rebuild and, like the 350 lump, we will be going into the detail of that work through the dark and cold winter months. Time now to look at the chassis and assess any work required there. Both front and rear brakes are, typically, seized solid and will need stripping and rebuilding.
The frame is in pretty good nick with just a small amount of corrosion around some of the welds so it doesn't warrant a total repaint. I will just try some rust remover and silver touch-up paint. The neglect and repair damage to various parts is all too obvious. Notice the wrong screws in the master cylinder cap for instance.
These also happened to be the wrong pitch thread and have been forced in, damaging the threads, although luckily not beyond repair. The wiring loom looks to be in fairly good shape however. There is copious amounts of insulating tape applied to the electrics, no doubt in an attempt to weather-proof them.
This is not very efficient as water can penetrate the tape and then stay there to corrode the contact points, causing more mayhem than if left open to the elements. The only real result of this one big sticky mess is that the glue will separate from the tape and be easily removed with a bit of solvent to leave us with a clean and tidy loom.
So the bike can start to go back together, the boxes full of parts can be emptied and I can start the plumbing nightmare that is the reassembly process. Remember there is four of everything in a very tight space indeed so the need to get the cables and pipes in the correct places is absolutely crucial.
Chris Pearson