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Yamaha YDS7 250cc

Yamaha YDS7

Motorcyclist Illustarted 1971

Ooce upon a time there was a motorcycle factory which made ordinary motorcycles and racing motorcycles. Their name was Yamaha. Other people made motorcycles too, and they all were very similar. The other factories stopped making racing motorcycles because it cost a lot of money, and nobody, especially the Rich Americans, seemed to take any notice anyway, and for a long time all the different motorcycles remained alike in so many ways.

Yamaha kept on making racing motor­cycles, and shortly, they made the best racing motorcycle, so everybody rode them, and everybody noticed. A lot of people grumbled because they were so good. There was nothing else to look at on race days they said.

Yamaha became very wise in the ways of fast motorcycles, so they quickly understood that what is good for racing motorcycles is usually of great benefit to ordinary motorcycles, so although their ordinary motorcycles looked the same as everyone elses, they were not. All the others were very good, but they remained very good. Yamaha were very good, but got better, until they were very, very good indeed.

One day, perhaps, everybody will notice, and then a lot of people will grumble because . . .

Neither Alan Aspelf'-'nor I can find a single valid point on which to hang any criticism of the DS7, which speaking personally is disastrous, because con­structing any test without some good solid criticism is rather like eating a meringue. You know it's all sugar, because that is what it is, all sweet and lovely, but somehow, vaguely un­substantial. You get to the end and feel you have missed something; you know what I mean?

Not, mind you, that the little Yamaha was unsubstantial, far from it, but it was so good as to make it almost (but not quite) uninteresting. Dammit, what can I say about a 250 that has the ability to outperform its rider(s) in every respect? You name it, the Yamaha did it, and always with a reserve in hand.

As far as I can remember, this is the first Japanese machine I have ridden that has proved to have frictional qualities equal to European ones. Things like tyres, suspension damping, and brakes. Most of them fall down in one or other aspect, even the Honda Four, till now, top contender, but in second place now.

I have stalled for long enough; on with the report.

Starting. Ah yes! Saviour of my test report. A fault! In the early stages of my short-term ownership, before I got the hang of cold starting,* it once or twice nearly proved to be the end of what was to be a beautiful friendship. It all started in Yamaha's garage at Camberwell, London, on the first kick. To cut a long story short, only one plug fired. I realised power was down, but put it down to the odd choke arrangement for cold starting, and by the time I understood that only one combustion chamber was doing its stuff, the dead plug was wet.

Back at the office, I. removed it, cleaned it, heated it, put it back, but might just as well have spent my time more wisely, for it remained dormant, the crankcase having a reservoir of unburned fuel' deposited in its right hand side. Simple. I thought, undo the plug and drain away the unwanted puddle . . . There is no crankcase drain plug ... To transcript my opinion of that would not only take too long, but would un­doubtedly prove libellous.

Should you find yourself in such a predicament with a flooded crankcase, I suggest that the best way to reclaim the lost combustion is to remove the fuel tank and battery, drain the carbs, stand the bike on its seat and handlebars, and pump the kick start for as many minutes as it requires to drain the engine of surplus fuel via the plug holes in the heads.

Alternatively you can risk your pistons and do as I did. As soon as you realise that one plug is wet and inoperative, do not stop the engine, but switch off the fuel tap, and ride the 'bike until it runs out of fuel completely. This might scavenge the crankcase without adding to it, and dry the plug. Once stopped, swap over plugs, putting the wet one in the hot head and vice-versa. On starting, they both should catch; if not, repeat the rigmarole until they do.

In the best Yamaha manner, the machine's top speed was not its out­standing characteristic, and was somewhat less than at least one com­petitor by a handful of speed measures. Top speed was 90 mph. Strangely enough, the speedometer proved to be completely accurate, whereas the rev-counter was fast at high engine speeds by 500 rpm. At 90 mph, it should have been indicating 8500 rpm, but was in fact quivering delightedly and optimistically around the 9000 mark. Exactly at what engine speed the error crept in is almost impossible to decide without many hours over the throttle and later as a desk, and for nothing really, for at 70 mph in top gear the revs corresponded accurately with the speedometer, showing 6700 rpm on the clock.

The manufacturers claim that maximum power is produced at 7500 rpm. I would argue the point. Most two-strokes' power delivery falls away rapidly once engine speed increases beyond maximum power output. The DS7's did not, but kept on running until somewhere between 8000 and 8500 rpm. (The elastic guess being due to rev-counter inaccuracy.) Even above this, power was still coming in strong and clear, but without quite the same urgency. In the lower gears, the rev limit was governed by common sense and respect for the machine rather than the limita­tions of the combustion process.

Quite enough power was forthcoming from the square twin from 2000 rpm to be usable in the lower gears for town work, but the top two required another

1000 before any accelerative response was noticeable. From about 3000 revs, the power increased progressively until at 5800, a surge of extra bhp got into stride and added to the fun. Holding the engine speed above this kept the roadspeed high enough to deal with anything that came along, including an R69/S BMW, who in the end admitted his inferior performance to the Editor - - who was riding the Yamaha at the time — by resorting to desperate overtaking measures in town limits. Poor show, that.

Front wheel lifting, or more accurately, skittering, was all part of the process under hard throttling, but due to the race-worthy roadholding of the frame was scarcely noticed, unless the thing was exaggerated deliberately. It was advisable, however, to sit as far forward as possible, and lean over the bars from a maximum effort sprint. Gear speeds at a true engine speed of 8500 rpm were: 1st, 44 mph; 50; 62; 75; 90. These are not the speed ceilings though. They, besides being very difficult to pin down exactly, are im­practical due to the immense power fall-off at the limit, especially in the higher gears, and dilute acceleration in their accomplishment.

Road performance has been increased by Yamahas' deliberate undergearing of the machine. Initial acceleration is im­proved, and so is lapsed time to top speed. Unlike most small-engined 'bikes, the DS7 hits the upper 80s without pause, and only slows, even in top gear, once over the power top, near 90 mph, hence its incredible ability to outperform bigger engined machines with such sim­plicity. Perhaps a private owner, especi­ally a smaller chap, might prefer to raise gearing a little, and save on wear, tear and fuel without sacrificing much to maximum speed.

Induction silencing was good; no carburetter roar being audible at any speed. The engine itself was com-mendably silent too, completely lacking the restless milling of so many two-strokes on tickover. Two-stroke silencing is so much a matter of opinion that no statement can be more than an opinion, but certainly the Yamaha's exhaust gases escaped with no more noise than any other machine's, and at speed was deeper, and so pleasanter, than the majority of two-strokes.

However good was the engine's per­formance, it was outmatched by two others, the roadholding ability of the frame and suspension, and the brakes. They were simply marvellous, for no matter how fast an engine might be, if the rest of the machine cannot handle its power then it might as well not exist. Yamaha have, in respect of the machine's rideability, paid at least as much atten­tion to the pycle parts as they have to the engine; maybe more. completely safe. It is not exaggerating to say that faster, safer cornering on any other roadster would be near impossible. Braking partnered the handling and roadholding superbly. While the rear one was very good, as indeed most are, the front one was beyond reproach.

As proof (to my mind) of the frame's true merit, not even the vast Ajrierican handlebars upset the handling. At the highest roadspeed the machine's wheels remained perfectly in line, regardless of the surface irregularities. Both the front and the back end stayed exactly where they were meant to, without a moment's hesitation or unwanted movement. Of course, because of the touring comfort setting of the suspension, mainly on the rear, at the ultimate cornering speeds some pitching set in, but without any sympathising from the frame. Pitching, if you demand comfort, and who does not, must be expected on roadsters, especially small ones. Although softly sprung, the be indulged in, but .it required a very deliberate effort, and was nevertheless smooth and receptive, showing no desire to grab. While at maximum speed, it would set the tyre squealing if needed.

The electrical system behaved itself impeccably, and appeared to contain careful thought and design. All the switches were well placed on the left-hand handlebar, and required little more than thumb movement to activate them, liven the ignition switch was above the tank for a change, between the instru­ments. I do so hate the idiotic placing of it underneath it, as is so common nowadays. The headlamp beam was good without being exceptional.

Seating and riding position were com­fortable except for the style universally adopted as normal by the Japanese. Footrests were too far forward, and the bars too high and wide, but that is personal. Within their fashion they were excellent. The fuel tank was too narrow for an upright riding stance, but would be well shaped for an English attitude.

I was not over enthusiastic about styling. It was fussy, almost Victorian, with far too many fiddly do-dans scat­tered around. Matt black, polished alloy, and red circles cast into the crankcase, chrome flutings on the side panels, white broad lining on the tank; it was too much of a good thing. The lines of the machine were great, almost ageless in fact, and that is difficult to achieve.

By no means the least expensive 250, the DS7 is unarguably one of the best. Its performance abilities cannot be graphed, but only understood on riding. Then does the company's racing interest show itself.

Mere fun riding cannot justify the DS7's considerable ability to return an out­standingly fine performance, with a rare consistency. Like still waters, the middle sized Yamaha runs deep, and requires hard, ultra-fast riding to bring out the best.

Yamaha YDS7 Specification;

Engine:

Capacity, 247 cc. Bore and stroke, 54 x 54 mm. Construction, all aluminium. Porting, piston controlled, five port type. Crankcase, hori­zontally split, also gear case. Crank shaft, built-up construction, with centre -main bearings and oil seals clamped between crank-case halves, and pinned and dowelled in place. Four main bearings, one either side of crank-pins. Main bearings, ball race. Big ends, needle roller. Small ends, needle roller. Connecting rods, steel. Big ancfsmall end eyes act as outer bearing races. Pistons, two ring type, "Teflon" type coated to inhibit running in seizure likelihood. Compression, measured from closure of exhaust port, 7.1:1. Claimed power, 30 bhp at 7500 rpm. Torque, 2.92 kg/m at 7000 rpm.

Carburation:

Twin Mikuni instruments. Throat size, 26 mm. Cylindrical throttle valves, main jet fed direct from underhung, integral float bowl. Air cleaner, cartridge type paper element. Cold start device operated on left-hand side car­buretter only, right-hand carburetter connected by balance pipe only. Yamaha claim this sufficient "choke" for right-hand side instru­ment.

Lubrication:

Force feed, metered injection into induction tract only. Pump, gear type, driven from right hand end crankshaft, controlled by throttle opening. 160 miles per pint recorded during test period, including commuting, high speed touring, and speed testing. Tank capacity, 4 pints. Quality recommended, two stroke or straight oil only,'not multi-grade. Transparent inspection window let into side of oil tank as level check.

Electrics:

Battery, 12 v 51/2 a.h. Generator, 100 w alternator mounted on left-hand end crank­shaft. Maximum power developed at 2000 rpm engine speed. Energy transferred through single brush pick-wfLjrom brass face slip ring. No permanent magnets* Rotor segments are only mag'netised from battery current, by activating ignition switch. This system ensures a better and more consistent plug spark when starting over long periods of time due to difficulty in manufacturing permanent magnets, and high cost of same. Ignition, twin coil and contact breaker. Lighting: Headlamp, 35/35 w. Rear and stop lamp, 6/21 w. Flashers, 27 w. Also: main beam, ignition, flasher, and neutral gear indicator warning lights.

Transmission:

Primary drive, helical gear on right-hand side. Clutch, wet multi-plate, incorporating coil spring shock absorbers. Five speeds, up-for-up gear change, left-side foot lever. Rear drive: chain, including rubber vane cush drive in rear hub. Gear ratios, 1st, 13.66:1; 1254; 10.07; 8.24; top, 6.90.

Fuel:

Tank material, steel. Quantity, 2 gallons, plus 3 pint reserve. Consumption, 41 mpg over duration of test, including commuting, fast touring and speed tests. Slower riding improved, matters up to 63 mpg. Four star fuel used throughout test, but three star adequate pro­viding slow speed, heavy traffic density riding not indulged in, which caused plug sooting.

Frame:

All welded, mild steel tube. Twin lower loop, single triangle braced upper. Heavy gusseting around head, including fabricated, extended sleeves welded to down tubes as stiffeners. Rear end triangulated.

Suspension:

Front, hydraulically damped, tele-fork. Rear, hydraulically clamped, pivoted fork, three way adjustable for load. Bronze bushed pivoted fork bearing, grease lubricated. Steering head bearings, surface ball race.

Wheels:

Both 18 in. Tyre, front, 3.00 in. ribbed. Rear,

3.25 in. zig-zag. Both nylon corded Dunlop.

Brakes:

Front, 7V4 in. tls. Rear, 71/z in. sis, rod operated by right-side foot pedal.

Dimensions and Weight:

(claimed) dry, 304 Ibs. As tested with full tanks, tools, road dirt etc., 338 Ibs. Seat height, 31 in. Wheel base, 52in. Ground clearance, 6 in.

Price:

£343 including delivery charge

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