|BOOM CONDITIONS that now vitalise the motorcycle industry are partly the result of a lot of people discovering that bikes are fun, and partly due to the subtle promotional efforts of the Japanese manufacturers. With skillfull advertising, these factories made cruising the highways on a colourful, chromed motorcycle seem a great way to spend an afternoon.
Yet the demand they created is a double-edged weapon. It encourages manufacturers from almost a dozen other countries to contest the prized U.S. market, and insures that a bike has to be good before it will sell in volume. Thus, progress in design is one of the keys to a fat order book. In the past decade. development of engines, frames, materials, quality, and durability of components has surged forward, but probably the greatest progress of all has been in the two-stroke engine.
Suzuki set the pace in production of 250-cc sports two-strokes with its X-6 Hustler. Its startling performance, six-speed gearbox, and impeccable handling set the standards by which most other 250s were measured. Here was an impudent new breed of two-stroke, a bike that could compete with machines of twice its piston displacement.
The Hustler also possessed its faults. Probably its greatest disadvantage was its narrow spread of power, which insured that the rider made continual use of all six ratios in the gearbox. Now, that same process of development which evolved the Hustler, has produced Suzukis T305 Raider, a bike with as wide a spread of power as any machine in its class. The six-speed transmission remains, and the additional 55 cc mean a bonus in top end power. Its just that excitement starts with the tachometer needle much lower down the scale.
|Suzuki has invented the phrase Vol-U-Matic to describe certain of the changes that have produced the wider torque band. The name sounds technically intriguing, as are the modifications behind it. Rather than adopt disc valves or extra transfer ports for its road machines, Suzuki instead has experimented with the standard features of conventional piston port induction, and the conventional number of transfer ports.
Most startling of the features incorporated in the new modifications is the size of the carburetorsa wacking 32 mm in bore size. Such giant diameters normally are associated only with racing machinery, and indeed, the majority of bikes in the Raiders displacement class use carburetors varying from 24 to 28 mill. Obviously, large throated carburetors offer a large increase in mixture induction at high engine speeds. But dont they also hamper low speed engine operation? Generally. yes, but in Suzukis case, no. Other factors offset the 305s 20 percent increase in carburetor and intake port diameter over the 250. In the first place. the 305s induction passage length has been shortened by almost 20 percent over the X-6, allowing a closer relationship between engine and carburetor. At part throttle openings, there is no lag in engine response. Also. intake port opening duration is considerably changed. The 305s port duration actually is shorter than the 250s124 degrees compared with 148 degrees. Normally, this shortening process would indicate improved torque at the expense of top end power. but Suzuki has offset this by increasing the 305s total intake port area to 810 sq. mm. The equivalent figure on the 250 is 774 sq. mm.
The carburettors on the 305 are identical in principle to the units, previously termed altitude-compensating, found on the 500/Five and 200-cc X-5. The compensating carburettor differs from standard practice in that a small external tube connects the carburettor intake to the top of the float chamber. The pressure in the float chamber is always less than atmospheric pressure when the engine is operating. At low engine speeds, most high-revving two-stroke engines reject some of the air in the incoming fuel/air charge. This causes an increase in fuel in proportion to air. The result is a performance-dulling, over-rich mixture at low engine rpm.
Because pressure in the float chamber is relative to the negative pressure in the 305s carburettor intake, there is reduced pressure in the float chamber. Thus float chamber pressure is inversely proportional to engine rpm. The result is a reduced fuel flow through the carburettor main jet at low rpm. This reduced fuel flow corrects the tendancy toward over-richness of the fuel/air mixture at low engine speeds, and mixture progressively richens as rpm build up. The Raiders engine is evolved from the X-6 unit. Increased piston displacement is obtained by wider cylinder bores, an oft-used method of gaining entry into a larger machine class. In place of the square cylinder dimensions of the 250-cc engine, the Raider retains an identical stroke, but bore rises by 6 mm, to 60 mm. Other changes include modified combustion chamber shape from squish type to hemispherical, in-creased cylinder finning area, and refined piston profiles and modified piston clearances, for quieter engine operation. Problems with the early X-6 Hustlers also occurred in the transmission. Riders discovered that missed changes were frequent. through no fault of their own. This was a pest in normal running, but became a positive embarrassment during a fast ride, when a false neutral instead of a gear would allow engine rpm to soar alarmingly in a split second.
Modifications have eliminated the problem, and during the entire test period not a single unwanted neutral occurred. Lever movement is positive, and very brief. Changes can be snaPped through with hardly an interruption of drive to the rear wheel. This improved shifting has been achieved by the use of four shifting forks, in place of three, to actuate the gears. Also, gear tooth profiles have been redesigned. A reversal of policy that may not please some Suzuki supporters is that while the X-6 featured a shifter shaft that extended on each side of the transmission casings, the Raiders shaft is exposed only on the left. Consequently, anyone who buys a Raider, but prefers to effect gear changes with the right foot, will be forced to learn to use his left boot. Clutch action is improved by the use of a synthetic anti-friction coating on the cable, providing less lever effort and smoother operation. Clutch cork plated working area has been increased from 43 to 48 sq. cm.
"Posi-Force" engine lubrication has been a Suzuki trade-mark for some years now, but on the Raider the system takes a step forward efficiency. It now is similar to methods introduced on the X-5. Pistons, connecting rod small ends, and cylinder walls. now are provided with a separate supply of lubricant. Previously, these components had to rely on oil thrown upward from the crankcases The engine-driven oil pumpwhich also is mated to throttle openingdelivers oil through a pair of tubes, each of which divides into two. Thus, two pipes divert to the left side of the engine, and two to the right side.
On each side. one pipe leads directly to the rear cylinder wall. The other pipe runs to the crankcase, where drilled passages admit lubricant to the main hearings, and big end bearing of the connecting rod. From there, oil mixes with incoming gas, and eventually enters the cylinder barrels. Advantages of feeding oil directly to the critical piston skirt area are that the total amount of engine oil required is considerably less. Oil mileage is thus increased, the exhaust system runs cleaner, and spark plug life is lengthened.
On the road, the modifications to the engine and carburettors immediately are apparent. The machine idles quietly and without fuss, and the engine offers forceful yet smooth power from as low as 2000 to 3000 rpm, depending on which gear is engaged. Compared to the 250, the Raider feels less a racer, more like a fast but effortless-to-ride road bike.
Its still possible to play racer-like games with the gearbox while flicking the bike along a curving road, but the beauty Ok the Raider is that this type of riding is not a necessity. Fast travel also can be achieved by using the engines wide spread of power. Hills and headwinds are less of a problem than they are to the 250. The Raider will maintain a sixth gear cruising speed of 65-75 mph up quite severe gradients and into stiff winds. Its 250-cc companion frequently requires a shift to fifth, or even fourth, to hold speed under such conditions.
|Quarter-mile times for the Raider are respectable,without being sensational. However, the very wide handlebar affected its performance at the upper end of the speed scale. Its only fair to say that the bike possesses adequate power to master any situation that arises on the road. That handlebar, incidentally, was very comfortable, despite its excessive width.
Two separate instruments, a speedometer and a tachometer, are mounted fairly high, so that they easily are read. Both dials are large, and the speedometer, on the left, also incorporates an odometer. Along the lower part of the tachometer are mounted three warning lightsone indicating neutral position in the gearbox, another informing that headlamp high beam is in use, and the third an indicator for flashing direction lights. Because flashers were not fitted to the test bike, the light remained inoperative. Not only are the dials effectively mounted. but they remain totally unaffected by vibration, and the needles are as steady as a marksmans aim.
Frame construction is typically Japanese, with its sturdy configuration, and glossy black finish. The down tubes spread very wide before passing under the engine, and leave plenty of room for the exhaust pipes to exit in the space between them. Twin toptubes extend rearward from the down tubes. and are met under the fuel tank by another tube running from the upper steering head. All junctions at the steering head are heavily gusseted, providing a very firm structure.
Foot pegs are solidly mounted on outriggers bolted at two points to the main frame. The passenger foot pegs follow conventional Suzuki pattern in that they are very short, and recessed into the top of the exhaust silencers. Despite their size, they offer sufficient room for boots or shoes. Adding to the attractive styling are handsome chrome plated fenders, and steel gasoline tank and side panels in a lustrous blue paint finish. A competition orange colour scheme also is available.
The T305s fuel tap is an unusual and ingenious little feature that includes no off position. It incorporates a chamber. diaphragm. valve, and valve spring, while a length of tubing links the chamber and the left carburettor. When the engine is running, vacuum generated in the carburettor is transmitted to the chamber, and pulls the diaphragm and valve against the spring, leaving a gap for fuel to exit from the tank. When the engine is cut, the spring snaps the valve shut. Advantages of the system are that the possibility of flooding is reduced, the fuel tap does not have to be adjusted when the bike is parked and restarted, and in the event of a fall, there is no danger of a fire. The tap includes a conventional reserve position, and also a priming setting. The latter enables fuel to bypass the diaphragm chamber if the machine is to be started after a long interval of disuse.
Suzuki engineers have worked skillfully at producing the Raider. Its a bike with more charm and versatility than the Hustler, and proves equally acceptable as a ride-to-work machine or as a long distance tourer. The factory is fairly late in entering the 300-350-cc displacement range, but the final product is going to win many friends.