MOTOR CYCLES

Press, 28 October 1982, Page 27

MOTOR CYCLES

Water-cooled trail bike

(By PETER BRITTENDEN) Moto-cross technology has been used in the production of Yamaha's latest trail bike, the water-cooled DTI2S.

The styling and mechanical features of the DT are similar to those found in the Yamaha factory's moto-cross racers — the YZ range. Normally, any street motor-cycle is simplicity itself but Yamaha has incorporated many features of modern motor-cycle technology in this model. Apart from liquid cooling, the DTI2S has a counter balance shaft to reduce engine vibration, the 'Yamaha Energy Induction System, a patented method of ensuring smooth vapour flow between carburettor and cylinder, single shock-absorber rear suspension, and pointless ignition.

All this adds up to a pretty sophisticated package and the DT was fun to ride.

There, was only one problem — with power delivery. Inevitably, because of its small capacity, the 123 cu cm engine had a fairly narrow power band. Until the engine started spinning over 6000 rpm, not a great deal of power was available but, after ■ that figure, the performance improved. It would be easy to make too much of this situation. Useable power is available between 2500 rpm and 6000 rpm.

Yamaha says its Y.E.I.S. eliminates a narrow power

band and, in my personal experience, this is the case with the larger capacity twostrokes produced by this factory. But it would be difficult to produce a 125 cc engine with good performance and a wide spread of power. The DTI2S has plenty of power and a relatively narrow power band. In all its functions the engine performed flawlessly. Starting, thanks to the electronic ignition, is a onekick affair, despite the very short throw the kick start has.

Vibration is virtually nil at every engine speed — very unusual for a small-capacity two-stroke.

One of the nicest features was the quietness of the engine.

Water cooling helps here — allowing the engine tolerances to be narrower than with an air-cooled twostroke. As a bonus, Yamaha says the engine and radiator weigh less than the previous air cooled versions.

Comfort was an ingredient Yamaha paid plenty of attention to. The seat (red-on my white-tank version) was very comfortable and the handlebar controls worked really well.

Dog-leg shaped levers and the roll-up type of throttle were both a nice touch.

There were no problems with the transmission. All six gears engaged freely every time and the clutch action is very light. Although the forks are not

air assisted, they work very well with virtually no "hesitation" on rough roads or offroad. The rear "mono-cross" suspension was, as always, responsive with plenty 'of travel. Yamaha claim 230 mm fork travel and 200 mm rear suspension travel - good for a small trail bike. The drum ’ brakes, front and rear, provided no problems. Over all the DTI2S is a very' tidy package. For $1998 the buyer gets all the latest in motor-cycle innovation, a very comfortable ride, supple suspension, and plenty of power. The test machine was provided by Tommy’s Yamaha, St Asaph Street, Christchurch. Specifications: Engine, water cooled single cylinder, two-stroke; displacement, 123 cu cm; bore and stroke, 56.0 x 50mm; compression ratio, 7.2:1; maximum power, 11.8 kW at 7000 rpm; maximum torque, 16.0 Nm at 7000 rpm; carburettor, 24mm Mikuni; ignition, C.D.1.; fuel tank capacity, 9 litres; transmission, six-speed; length, 212 cm; width, 82cm; ground clearance, 27cm; dry weight, 97kg; front suspension, telescopic forks; rear suspension, monocross; brakes, drum front and rear; front tyre, 2.75-21; rear tyre, 4.10-18.