The Motorbike Archives

Well, the real item is considerably different than either rumour would suggest. It's a dual-purpose 250cc thumper that is without a doubt the best off-road bike Honda has ever produced for sale to the public.

Honda's 250 Motosport looks a lot like the SL 125. It is an eye-catcher with gracefully flaired fenders and a tasteful gunmetal grey paint job. For street use there are lights, a horn, a tachometer, and a speedometer with resettable odometer.

For off-road buffs, the muffler/spark arrester combination is high mounted and tires are of the classic dirt 21-in. front/18-in. rear combination with round profile universal tread. Because all the accessories detach quickly, Honda is offering the best for both on-and off-road riders.

Appearance aside, the Motosport's biggest selling point is the engine. Being a four-stroke, it is ideal for street use or for that occasional trek down Baja where suitable two-stroke oil is nonexistent. And, like other Hondas, it is mechanically quiet in spite of its sophistication.

Honda has retained the single overhead cam configuration for the 250, but head design is considerably different, from anything produced previously. There are four valves—two intake and two exhaust. The primary advantage is increased port area without adding weight to individual components. A single intake valve of comparable area, for example, would be considerably heavier, and at higher rpms would be less reliable because of additional stresses caused by the increased mass.

Because of the large valve area and sporty cam grind, the Motosport Single will rev to 8500 rpm. But, don't get the wrong idea. The unit is not fussy in the least and its tractability must be rated as outstanding. Sufficient power for climbing hills is available from 1500 rpm or so and there are no flat spots in power delivery right up to redline. The more rpm the engine is turning, the more power is on tap. Bhp figures have not been released yet, but the oversquare Single (bore and stroke is 74 by 57.8mm) is definitely no slouch.

In spite of the desirable power characteristics, though, most medium and large displacement Singles suffer from two problems: they are hard to start unless one knows "the drill," and they tend to vibrate a lot at higher rpm. The reason we say most is that Honda has seemingly solved these problems, also.

If the unit is cold, pulling up on the handlebar-mounted choke button, cranking the engine over until it comes up on the compression stroke, and giving it a swift kick brings it to life. What's more, the primary kickstarter, which allows the Honda to be started in any gear with the clutch pulled in, is easy to depress even though the compression ratio is 9.3:1. As for vibration, it's absolutely minimal and compares favorably with anything else in production today.

A lot of credit for the machine's smooth running and ease of starting must go to the Keihin carburetor, which is similar in design to the units fitted to the CB 500 Four. The throttle linkage on these carbs is interesting because it consists of two cables instead of the usual one. The second cable allows a push-pull arrangement which both advances and returns the slide. This facilitates minute changes in throttle and is especially useful in slow sections. On conventional setups, the slide is returned by a spring which is definitely less positive in operation.

To keep things running cleanly, Honda has designed a good air filtration system for the Motosport. The wet, polyurethane foam filtering element is protected from water and excessive dirt by a plastic air-box. Air is ducted into the box through a screened intake located under the seat.

Honda's claimed top speed of 80 mph seems reasonable, as Motosports have wide-ratio, five-speed transmissions. Low gear is a little on the tall side for slow trials-type going, but most riders will probably leave the overall gearing as is because of the engine's ability to plonk along at incredibly low rpms. Gear spacing is excellent and shift lever travel is minimal. Like the transmission, the clutch is very light in action and is capable of withstanding repeated abuse.

The Motosport powerplant is totally new in design, and for a change the same can be said of the frame. Most Japanese off-road bikes are products of the short wheelbase, high ground clearance school of design. Bikes of this type tend to be highly manoeuvrable at low speeds, but handle very quickly and in some cases are unstable in the 50 mph or above range.

Fortunately, Honda has changed over to the European long wheelbase, low center of gravity theory, and as a result the Motosport (with a 56-in, wheelbase) tracks well at any speed. The front end feels a trifle heavy but actually the Honda is well balanced. It has absolutely no tendency to wheelie when climbing hills and always lands rear wheel first following jumps.

Some credit for this must go to the rear damper units which are also new. The shock itself offers adequate damping and, like the Koni, the shaft is fairly large in diameter, which should prevent bending.

Two springs are fitted to each unit. The top one is rather long and has a different spring rate than the shorter bottom spring. In combination, they have characteristics similar to a single, progressively wound spring. The shocks are five-way adjustable and on our prototype had to be set on the stiffest spring position to avoid bottoming. Honda will no doubt fit slightly stronger springs to production models.

Front forks are excellent. Of the now classic Ceriani design, they have over 6 in. of travel. Bottoming does not occur, even when the Motosport is forced over rough terrain. Likewise, damping is right on and adds to the bike's fine handling.

So far, the Motosport sounds interesting, but rather typical. By this we mean that it is well designed for its intended use and is well made. This time, however, Honda has gone one step farther. They have made an obvious effort to reduce weight. The prototype engine weighs only 81 lb. Then there are light conical hubs to reduce unsprung weight and sturdy plastic components like the air box to aid in maintaining as low a center of gravity as possible.

Weight of the prototype is 268 lb. dry. Lighter engine castings on production models, though, may lower weight somewhat. The final figure is hard to predict, but Honda engineers have promised a Motosport that weighs 1 lb. less than the current 250cc Yamaha Enduro.

The production version should be well received. The 250's weight rivals that of an equivalent two-stroke, and it promises a minimum of mechanical hassles.

While its peak power falls somewhat short of levels achieved by the current crop of 250cc two-stroke enduro machines, it has them beat for flywheel effect and bottom-end torque. Combine these with whispering silence and good handling, and you have an instant best seller.

Just when we thought the era of four-stroke Singles had ended.■