Yamaha Rd250a

YAMAHA RD250A

Cycle World Road Test

Need An Economical, Reliable And Fun Second Car? This Might Be Just The Ticket!

YAMAHA’S ALMOST complete domination of Class C 250 road racing and Novice flat track events is legendary. The lightweight TD, and now the waterpumper version of the Yamaha 250 Twin, has been nearly invincible in all forms of competition in which it is entered.

As you’d expect, it’s pretty difficult (and costly) to get hold of one of these racers but Yamaha has nearly always made a purely street version available to the general public...a street version which incorporates many of the features designed specifically for competition. r> e RD250A is no exception and shows its racing heritage strongly in several important areas: styling, design, performance, and handling qualities.

Styling wise, the machine is slim, lean, and businesslike, at least as far as Japanese machines go. There is almost an absence of useless chromed frills to dazzle prospective customers. Instead, we find a clean gas tank, much like the one fitted on earlier Triumph Trophy models, which blends in nicely with a long black saddle, black engine package and conservatively contoured chromed fenders.

The RD250A engine is significantly different in appearance from the earlier YDS-3 Yamahas, and is quite different on the inside, too. The horizontally split crankcase assembly has been slimmed down significantly, the bore/stroke ratio is now “square” instead of “oversquare” (bigger bore than stroke), and there is a sixth speed in the transmission. The crankcase, cylinders and cylinder heads are now finished in a matte black paint, with polished fin edges and raised, polished lettering and accent strips on the crankcase edges. It is truly a handsome package, and one which is quite a bit smaller in bulk than the earlier Twins.

Oil for the transmission and the clutch is contained within the crankcase and oil for engine lubrication is delivered from a separate oil tank through the intake manifolds via a plunger pump whose delivery is dependent on the throttle opening and engine rpm. This oil mixes with the incoming fuel/air charge and is circulated through the engine, lubricating the connecting rods, pistons and central main bearings.

The biggest difference from earlier Yamaha two-stroke Twins is the incorporation of a reed valve induction system. In this system, there are seven ports in the cylinders which control the circulation of the incoming fuel/air charge after it has passed through the reed valve. But the inlet charge is controlled by the reed valve rather than the mechanical opening and closing of the inlet port by the piston’s moving up and down, or by the opening and closing of a rotary valve. Therefore, even if you turn the throttle open wide at low rpm, the engine will accept no more fuel/air mixture than it can use through the reed valve.

The 7th port is actually an extension of the inlet port and extends upward into the cylinder. This “port” improves performance by allowing more fuel/air mixture to be “rammed” into the combustion chamber and by simultaneously improving the removal of burned exhaust gases. This system yields smooth throttle response and aided in our obtaining a 58 mpg fuel consumption figure during ordinary street and highway riding. The fuel economy is fantastic; but there is one problem. Visible smoke. Our test RD smoked enough to make us self-conscious. Leaning the mixture out slightly would help, but more needs to be done than rejetting to cure the problem.

The crankshaft assembly rides on four main bearings so it won’t flex under high rpm loadings, and the clutch is driven from the crankshaft by a helical cut gear for mechanical silence. Clutch lever pressure is remarkably low and no slippage was noted, even after a hard day at the drag strip. An adequate clutch is particularly important on a 250 roadster as starting off when packing double requires “riding” the clutch in order to keep the engine from balking. >

Still, the clutch had an annoying characteristic. It was a little “chattery” when taking up the drive. This characteristic is often present in new machines, and more often then not it disappears as the clutch beds in. Our machine was getting smoother, but it was still a little jerky in taking up the drive, right up until the end of the test.

In typically Japanese fashion, the transmission mainshaft and layshaft are located one behind the other in a horizontal plane. The shifting drum and four girdling-type shifter forks are located below the transmission shafts. This shifting setup is employed on almost all motorcycles produced today, and works extremely well on the Yamaha. The gear ratios are necessarily spaced rather close together because of the power characteristics of the engine, but shifting is a delight. Moving from gear to gear requires minimal effort and gear lever travel is short.

Just sitting on the firm seat and grasping the narrow handlebars indicates that the RD250A was intended for some aggressive riding. One ride on a race track confirms it. Yamaha has a handler in the RD250. Really, it’s a bike that begs to be pushed to the limit!

Fine handling qualities in this case can be attributed directly to the frame. Patterned closely after the highly successful Yamaha competition machines, the frame is a double downtube, single toptube design with a seat rail connecting up forward to the downtubes just below the steering head and extending rearward to provide a mounting platform for the seat and attachment point for the rear fender. Fabricated from mild steel, the frame is very sturdy in appearance and in fact. Flexing does not occur. Welding is a little crude in appearance, but penetration appears to be good.

Braking is another area in which the RD250A scores highly. Using drum brakes on both wheels, the bike has a brake swept area of 61 sq. in., which gives a brake loading of slightly over 8 lb./sq. in. with a 160-lb. rider on board. Try as we might, we couldn’t get the brakes hot enough to fade severely, not even after several miles of downhill braking in the mountains. Brake pedal and lever pressures are only moderate, and braking “feel” is certainly above average.

Electrically, the Yamaha is above average, as well. Wiring is the plug-in type and almost all the electrical components are accessible for servicing by removing the alternator cover and raising the seat. The exception is the high tension coils which are located under the gasoline tank, but they rarely need attention, anyway. Lighting is on a par with other Japanese machines. The dimmer switch, horn button and flasher switches are located on the left handgrip and the lighting switch and an off-run-off switch nestle on the right handgrip. A nicely laid out instrument panel contains the speedometer and tachometer, turn indicator lamps, a headlight high beam indicator and a red light which tells the rider when the brake light is working. The neutral indicator lamp is inside the tachometer face, but it is obscured by the front brake cable.

The speedometer and tachometer are both large and easy to see, but sunlight reflecting off the faces makes them difficult to read at times. A non-glare glass for the lenses would be a> nice touch. Also, the rear brake indicator light and the high beam indicator light are distracting when riding at night. We feel they could be toned down quite a bit and still be visible during daylight.

YAMAHA

RD250A

$719

The underseat area is nicely laid out to facilitate servicing items located under it. At the front, near the gasoline tank, is an area for the toolkit. The kit contains all tools needed to perform routine service, but is only of mediocre quality. Under the space for the toolkit is the top of the air cleaner box, which is held on by a rubber strap that can be removed in seconds for cleaning or changing the air filter element. Just behind the air cleaner is the battery with its cell tops readily accessible for easy checking of the electrolyte level. And behind the battery is the oil tank filler cap. The seat, incidentally, locks, but not automatically, so the rider has a choice.

Riding the RD250A is a thrill. Starting from cold requires the use of the choke for a period of a minute or so to get the engine running smoothly. And then for the first few blocks, the engine is reluctant to accept large throttle openings. This hesitation disappears completely when the Twin reaches

operating temperature. Shifting the six-speed transmission is one ot the nicest feelings a motorcyclist can experience. Practically no lever pressure is necessary to snick the transmission from one ratio to the next, and all the other controls work so well that we couldn’t fault them.

But the RD250A is designed as a sports and commuting machine rather than a long distance tourer. The narrow seat is very firm and becomes uncomfortable after long periods in the saddle. The suspension is also a little too firm for long distance riding. Where the RD250 really shines is flicking it through corners on a winding, mountain road or it’s a good machine for small-bore production racing. There is very little engine power below 4000 rpm or so, and using the transmission is a necessity to keep the engine revs up in the power band.

The RD250A is extremely well balanced and leans readily in either direction. The side and center stands are easily accessible to the rider, but are tucked up out of the way so that they don’t drag when cornering. Nice! Charging through alternating right and left handers is easier than on any other 250 we’ve tested. Very little body english is required. Just pitch it in and gas it. Speaking of gassing it, the RD also pulls neat 2nd gear wheelies!

The seat-handlebar-footpeg relationship is very good for riders under 5 ft., 11 in., but even with one person on board the seat strap for the rear passenger gets in the way. Unless the rider is short, carrying a passenger over long distances will be uncomfortable.

As indicated earlier, the suspension is a little on the stiff side, but this permits the rider to negotiate high speed corners without the machine weaving or bottoming out over bumps. Like we said, the RD250A is a sporting machine with almost all the attributes one could ask for. But a long distance tourer it is not. For it’s intended purpose we find it difficult to fault. It’s one of the best, but its larger brother, the RD350, is an interesting piece of equipment, too, and only costs a few dollars more....