Kawasaki S1 250

Kawasaki S1 250 Road Test

Kawasaki S1“The handsome one”

During the birth of the modern day motorcycle, no one had any hard and fast ideas about its perfect shape and form. When Honda created the inline four cylinder Superbike in 1968, the rest of the leading protagonists shot off in different directions simply to avoid copying, all to return at some point, some within a few short years and others around ten years later. In between times all began creating various guises of machinery, lets just say it was hard to become bored with the variety on offer.

Kawasaki S1 250Kawasaki’s bent, following the crazy 500 triple of 1969, and with nothing but aged twin-cylinder two-strokes to call a small capacity line up, was to create a whole range of similar looking machines, all using the same basic layout of an air-cooled, inline, piston-ported, triple motor. The engine being the dominant feature of all of these new three-cylinder machines, sticking out level with the riders feet, and with a brace of exhaust pipes winding their way from the front of the cylinders down and under the cases before flowering into a lop sided array of chrome work by the rear wheel. One feature this new line up had that stuck however was the seat fairing, a common sight nowadays, but really advanced and radical thinking back in 1972, this plastic extension to the rear of the seat also allowed a small storage area to be built in as the 70’s biker found himself carrying bottles of oil and the like. This short period of design excellence aside , nothing else really stood out as advanced thinking, the chassis being of basic construction and, while the rest of the two wheel world was waking up to hydraulic disc brakes, the small Kwaks made do with drum stoppers all round, albeit with a reasonably powerful, 180mm twin-leading-shoe affair on the front. In 1973 the S1’s big bore brother the 350cc S2 did get the disc treatment but for some reason the S1 didn’t. This could have done little to help sales of the type in the UK as by this time the learner brigade had been introduced to this technology by other manufacturers, in fact the Kawasaki would have to wait a further three years for this to be implemented.

Kawasaki S1 250 TripleThe engine layout, with its smooth power delivery so typical of a 120 degree crankshaft, worked well with the larger capacity machinery in the range, especially the stunning H2 750, but when utilised in a smaller package the 250 and 350 versions were left wanting, still, it was enough to make the Kawasaki two stroke range stand out from the twin cylinder bikes of Yamaha and Suzuki, certainly in looks, even if the performance was left somewhat lacking. The Kawasaki triple engine is standard fare for any one who has ever stripped a horizontally cast power plant. The gears sit in the bottom case along with the crank with just the added cylinder sticking out on the timing side. Twin lipped, rubber seals provide the seals between each crank, this adds to the friction losses greatly, Yamaha had a lot of things right with their frictionless, labyrinth seal design but, of course this couldn’t have been used, even if patents etc allowed it, due to the uneven firing order that would see one side of the crank with a differential in pressure to the other two. Instead Kawasaki chose to run straight cut primary gears, these are far noisier than the opposition helical designs but at least they transferred the power from the crank to the gearbox with minimal losses. The outright power was there, the S1 produced around the same as the equivalent Suzuki and Yamaha 250’s of the period, but the internal friction losses were higher and the peak torque far lower. The result is a peaky engine that never really gets a move on until the revs are way up around the dusty end of the tacho and to keep it on the boil does take some fancy clutch and footwork, not really the stuff of the learner market place.

Kawasaki S1 250 triple engineGetting a leg over the S1 reveals it to be a small machine, the engine dominates the image but, once sat in the low saddle it is barely noticeable. A short prod to the kick-start lever has the triple burbling away, unevenly at first as the pistons and rings heat up and swell to fit snugly in the bores but, within a few short blips of the throttle, all is well and the engine happy to go. Select first and start to release the clutch to provide forward go and it soon becomes clear that at low speed and in traffic the clutch lever is going to become a close friend. It feels like an age until it can be fully released or risk stalling the engine. Anywhere below 6k on the tacho is of little use in the real world, its ok if you are in second or higher as a quick stomp down on the lever has the piston-port engine buzzing and raring to go but, if you are already as low as you can go in the five speed box, it is time to call on your new found friend, the clutch for some help getting away.

S1 250 TripleAlthough the sound the three pipes makes is a speedy one, on the road the S1 doesn’t feel fast and that is simply because it isn’t, top speeds near the ton have been claimed but in reality high 80’s and low 90’s are the norm for a well cared for S1 or KH250, and way less than those figures if ridden two up. A standing start from the lights will have the Kwak lagging behind too, with a standing quarter around the 17 second mark the triple is likely to have a good go at the Honda twins of the period but anyone with any sense would shy away from taking on the RD and GT at their own game. Even then when well on the move it is still a good idea to give those two a wide berth as they excel in all areas except looks, park up alongside outside the chippie by all means but, when the engines fire up, find a good excuse and head the opposite direction, or even better still stay behind and talk to the girls at the bus stop about how nice the bike looks.

Kawasaki S1 250 Road TestSharing the same chassis, engine bottom end and dimensions as its larger capacity brother, the 350cc S2, the baby of the three-cylinder family is too heavy for the few horses it does create. There is no power to be had, or used in anger, below 6000rpm and even then things are a little slow developing, the engine starting to show some interest around the peak of the torque before running out of puff less than a grand later. Keeping the engine on song with three of every thing to contend with was never an easy task, the slightest upset in multi carb and contact breaker set up would create an uneven engine and considerably sap the power, the difference between a finely tuned and not so fettled version is immense when sampled alongside each other. Get it all right, stomping gears in as required and the cat takes off as if mildly scalded, however allow just one of the many permutations to wander out of sync and the disinterested pussy is left with a lot less go. The same can be said of the front brake too, get it set up as the book says and it is capable of a convincing stooping experience over short periods, let it wear or get out of adjustment and be ready for clean set of pants especially when trying to stop in a hurry from the bikes top speed.

The chassis is more than capable of holding the engine in check during normal upright use and, were it not for the pipes bulking up the midriff, the S1 would have a decent amount of ground clearance, as it is however, the Kwak does drag itself around corners when ridden with a sporting enthusiasm. This is no bad thing as it acts as a limiter to the way the bike is ridden, but it is a shame as the short wheelbase should have yielded a snappy and exciting ride however, at speed, and with fast changes of direction the bike appears to have a change of mind mid corner, the front end follows the riders inputs with accuracy but something is lacking mid chassis, it feels as if a small hinge is built in and the rear end isn’t so firmly attached.

Kawasaki S1 250 ReviewAs a bike of its generation the Kawasaki certainly had the looks to beat the rest, however the big K did chicken out when compared to the other motorcycles they had produced both at the time, before and since. Gone was the adventurous and daring ethos seen in the big bikes of the range; instead we got a mild mannered and not so hot 250cc machine that got slower as tie passed, no doubt the US market played no small part in this as well as the impending UK learner laws and Kawasaki simply milked the deign for all it was worth over the next 8 years until the type finally disappeared from the showrooms in 1980.

Kawasaki S1 and KH250 Timeline

1972 – S1 chassis number S1F-00001
The first of the quarter-litre triples and, with a claimed 30bhp, by far the most powerful. Kawasaki were keen to establish a reputation in the smaller capacity classes and thought the mini 500 would do just that. Front mudguard colour is matched to the bodywork for this early model.

1973 – S1A chassis number S1F-04691
A chrome front mudguard was the only significant external change, the S1A was offered in three different colour ways, however a drop in power to 28bhp was also implemented.

1974 – S1B chassis number S1F-12001
Now minus the friction steering damper but sporting a new design seat and the locking filler cap from the Z1. This model, with the new switchgear allowing the choke to be mounted on the left handle bar, was only offered in one shade, Candy Green.

1975 – S1C chassis number S1F-16300
The chrome side panel badges were replaced by stickers and the wheels now sported wider tyres with 3.25 and 3.50 front and rear respectively. Halibut blue being the only colour for this year.

1976 – KH250 A5 chassis number S1F-24400
Revised clutch actuating mechanism marked the major change for this short lived interim model, noise and emission regs started the decline of the type too as restrictive exhausts introduced across the triples range dampened the engines enthusiasm.

1976 – KH250 B1 B2 chassis number KH250B-000001
The steel fork lowers were replaced for lighter, alloy items that now sported a 277mm single disc brake grabbed by a single piston-floating caliper.

1977 – KH250 B2 chassis number KH250B-008601
Although externally identical to the B1 the total power was knocked down a further 2bhp to just 26, making competing with the ever-faster machinery from Yamaha and Suzuki even more difficult for the heavy triple.

1978 – KH250 B3 chassis number KH250B-018501
Minor updates, the shape of the seat, and a new design, triangular shaped, front brake master cylinder set this version apart from the earlier models.

1979 KH250 B4 chassis number KH250B-025001
The side panels were no longer colour matched to the rest of the bike, being finished in plain black, three scheme were offered White, Lime green and plain red although the latter is extremely rare.

1980 KH250 B5 chassis number KH250B-028701
The end of the line for the triple two stroke. Now offered only in Kawasaki racing green as a mark of their series of wins in the 250 and 350 world championships, the road machine bearing no resemblance to the race bike however. The KH was dropped from the side panel logos and now printed in large white lettering on the seat cover

Kawasaki S1 250 triple Specifications

  • Engine – air-cooled piston-port two-stroke triple
  • Capacity – 249cc
  • Bore & stroke – 45 x 52.3mm
  • Compression Ratio – 7.5:1
  • Carburetion – 22mm Mikuni VM
  • Max Power – 30bhp @ 7500rpm
  • Torque – 19 ft-lb @7000rpm
  • Ignition – contact breaker
  • Transmission – 5-speed wet clutch chain final drive
  • Frame – steel dual cradle
  • Suspension – 34 mm telescopic forks. Twin rear shocks oil damped
  • Wheels – 3.00 x 18 3.25 x 18
  • Brakes – 180mm twin leading shoe drum, 180mm single leading shoe drum
  • Wheelbase – 1375mm
  • Weight – 155kgs
  • Fuel capacity – 14litres
  • Top speed – 96mph

Kawasaki S1 250 Gallery

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