Kawasaki G31m Centurion
KAWASAKI G31M CENTURION
“An Absolute Jet On A Smooth Track”
CYCLE WORLD IMPRESSION
THE 100-CC CLASS in Sportsman racing has increased by leaps and bounds during the past few years. This is due in part to the increasing number of suitable machines available to the competitively minded enthusiast. The new 100-cc Kawasaki, designated G31M, is such a machine. It has the highest performance capability so far available in a production small displacement dirt track racer.
At first glance you do a double take, as this little bomb is the spittin’ image of its big brother, the 238 Green Streak. The gas tank is painted Kawasaki racing green and holds 1.7 U.S. gal. of 20:1 mixed fuel. Front and rear fenders are made of attractive, polished aluminum. The frame is a double downtube cradle, painted a gloss black. The finish on all components is of the highest order.
The alloy hubs are laced to steel rims front and rear. These units are fitted with Japanese Dunlop K70s, 3.25-18, at both ends. The traction provided on a hard packed dirt surface is excellent. The front forks are similar to the well known Italian brand in appearance, but did not seem to have enough rebound damping action. When traveling over rough washboard type surfaces, a slight topping out could be felt as the slider legs reached the limit of their extension. The rear dampers are sealed hydraulic units, with non-progressively wound chrome springs. The spring preload can be adjusted by simply rotating a camring located directly under the lower spring seat. Damping action of these units is fine. Spring rate is on the stiff side, a desirable trait on most smooth, fast tracks.
All in all, the bike performed best when zapping around Saddleback Park’s dirt roads and TT tracks. The motocross course made keeping the revs up on the power band rather difficult.
The single-cylinder two-stroke engine is in a class by itself when it comes to rotary valve 100-cc displacement production machinery. The performance out of 6.04 cubic inches and the rated 18.5 horsepower at 10,250 rpm is fantastic. The torque rating of 9.75 ft.-lb. at 9750 rpm accounts for the neccessity of keeping the wick turned up to stay on top of the power curve. A 24-mm throat diameter Mikuni feeds the rotary valve port, which, by the way, opens at 140 degrees btdc and closes at 70 degrees after tdc. Spark is provided by a flywheel magneto at 23 degrees before tdc, which never failed to provide fire for the B9H racing plug.
This amount of power is transferred via primary drive gears to a multi-disc wet clutch. Five constant mesh gears keep the rear wheel spinning with the following overall ratios: first, 28.55:1; second, 19.48:1 ; third, 1 5.78:1 ; fourth, 13.18:1; and fifth, 11.61:1.
Ideal transmission spacing allows the rider to cope with the narrow power band. When a gear change is made, the close-ratio five-speed gearbox performed faultlessly in keeping the engine up on top of the torque curve. The left-hand mounted foot shift lever worked like a charm, with only a slight touch of the toe necessary to engage the next gear. The shift pattern is typical of previous Kawasaki models in that neutral is found by stepping down as far as the lever will go. This pattern is one of the simplest yet devised to engage neutral. There are times when it is not desirable to be in this position. For instance, when entering a turn, if you jab down quickly for low, only to discover that you were in bottom cog and now have neatly selected neutral.
This minor malady can be overcome by paying attention to gear changes and becoming familiar with the machine.
When 18.5 blip is mated with 184 pounds of ready-to-ride motorcycle, the result has got to border on outright ecstasy.
The little Kawasaki G31M Racer certainly lived up to expectations. The home ground for our 100-cc test bike is the smooth, hard TT type tracks that are so popular all over the U S
The controls are well built and suitably mounted for an average sized rider. Tall racers will probably want to move the handlebars and seat to provide extra arm and leg comfort. The throttle action was so effortless that we suspected the cable of not being connected to the carburetor. This apprehension was soon squelched, as the engine fired with an ear-splitting rap from the high mounted expansion chamber.
A note on starting technique can be brought out in regards to choke lever location. A small pull ring can be seen alongside where the throttle cable enters the right-hand case. When starting, pull up on the ring to induce a rich mixture into the carburetor. This method of starting will force you to assume a “Daytona” racing crouch, just like the big boys do, which gets you into a state of mind necessary to make use of the full ability of the machine.
It is by no means a bike to ride one-handed while gazing about the countryside. Full attention is required, or you may find yourself applying bandaids to embarrassing rasp (sic) berries on various spots of your anatomy. This is not meant to belittle the handling qualities of the motorcycle, as it performs just as it was meant to, a quick powerful racer built to win. [O]
