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Memorable Motorcycle: Yamaha AS1C 125

Wednesday, August 27, 2014
I must confess that I am not much in favor of bikes or animals being given anthropomorphic values. Yes, I can go along with the idea that a Collie bitch has at least 11 times the intelligence of the average human, and therefore ought to be accorded equal, or even superior, status with Homo sapiens, but a motorcycle is a collection of metal and, left to its own devices, doesn’t do anything at all.

Sometimes that metal does become a thing of beauty and wonder and takes the rider to heights of ecstasy. Let’s hear a round of applause for the inimitable Matchless G.50.

On other occasions walking looks like a better option than being associated with some motorcycles I can think of. I would have to be stuck in the middle of the Gobi Desert, and freezing to death, before I would be seen on the unspeakably vile Greeves Sportsman or a Francis Barnett Fulmar.

However, every now and again my Protestant pragmatism fails me because I come across a bike so heart-warmingly cuddly and cute that anyone would want to have it sat on your knee, being stroked, while you both watched Marc Marquez do another MotoGP demolition job. Such a bike is the utterly adorable Yamaha AS1C.

By the mid-1960s, Yamaha knew a lot about making two-stroke Twins – stretching all the way back to its Asama volcano racer days. It could be argued, with a grain of truth, that the early Yamahas were more than a little influenced by the German Adler Twins but plagiarism is not an exclusively Yamaha exercise.

It could also be argued that the first true Japanese sports bike was the Yamaha YDS1 from 1959 and variants of this powerplant were used in everything from mainstream road bikes to sheep-herding utility machines and the iconic TD1C production racer – without doubt the best 250cc, over-the-counter racer of its day.

However, by the late 1960s, the Twins needed a complete revamp. Enter then the AS series and some of the best motorcycles ever to leave Japan.

It is worth remembering that by 1968, when the new Twins were introduced, two important milestones had been passed in Yamaha’s history. First, Yamaha had racked up five World Championships in the 125cc and 250cc classes and on the way had learned an awful lot about two-stroke engineering. Certainly, the Yamaha V4s, in both 125 and 250 guises, were outstandingly the best two-strokes of their time.

The Yamaha AS1C front forks and brake are from the FS1E 50.
Second, 1968 was the end of the classic era of racing when the lead footed bureaucrats in the FIM stomped all over technical innovation and dumbed down GP racing so that the maximum number of cylinders which could be used in a 125cc or 250cc GP was two, along with a restriction to six speeds of the gearbox.

Honda, Benelli and Suzuki all walked away from GP racing in disgust – but Yamaha didn’t. If two cylinders and six speeds were all that the regulations permitted then it would go racing with these restrictions – and win.

It was with this background that Yamaha launched its new range of Twins – ranging in size from the 90cc HS1 all the way to the 350cc YR2.

To be fair to Yamaha, there wasn’t a bad bike in the range but for many riders, the star was the diminutive 125 AS1.
First, the little Yamaha was a real head turner. The neat little twin-cylinder engine sits slightly inclined in the equally neat frame and you just can’t help liking the bike. The design is truly form begetting function in a most attractive way.

However, the 125 wasn’t just a pretty face. The most important element of the package was Yamaha’s use of “boost ports.” On a conventional two-stroke, without a reed or disc valve, a huge amount of fuel is wasted because of inefficient combustion. The Suzuki T500 I raced at Daytona managed a wallet-destroying 12 miles to each gallon of race fuel simply because so much gas in each combustion cycle was never used to its full effect.

Yamaha added two “boost ports” to the AS’ cast iron cylinder. These dramatically improved the scavenging of the engine and gave a significant increase in power and torque. Boost ports were nothing new in that Walter Kaaden had developed them fully with his MZ race bikes and a second form, designed by British engineer Joe Ehrlich, had been around for 10 years before the launch of the AS125. However, both of these two-stroke gurus employed boost ports as hand-crafted tool-room exercises, undertaken very slowly by skilled craftsmen.

What Yamaha did so cleverly was to mass produce the system so that race technology went straight into production machines. And the effects were dramatic. The little AS1 produced an astonishing, for a production road bike, 15 horsepower, and at only 8500 rpm.

As an indication of just how softly the road bike was tuned, Yamaha sold a GYT race kit which transformed the machine into a full-on track bike. The conversion included new cylinder heads, barrels and expansion chambers and, depending on how clever the tuner was, power now jumped to anything around 22 hp at 13,000 rpm. Just how good this power output was can be seen by comparing it to a 500cc Grand Prix bike of the day, like a Matchless G.50 or Manx Norton, both of which gave around 48 hp. This was double the power of the 125cc Yamahas – but four times the engine capacity.

The Yamaha AS1C twin-cylinder engine is a jewel.
In the real world, the AS1 road bike did have to be revved hard but it was capable of a genuine 70 mph and, better still, it was utterly unbreakable. The biggest weakness was the ignition timing which, in the days before electronic sparks, could wander and very easily lead to holed pistons. I had a Velocette Venom which was almost always in sick bay and the AS1 was my spare bike, which I rode ruthlessly and without mercy – and it never missed a beat.

A major contributory factor in reliability was the labyrinth oil seal which finally solved the problem of seal wear in multi-cylinder, two-stroke engines.

If the engine was good, the gearbox and clutch were its equals. The five-speed gearbox gave sweet and positive changes and the clutch was light and fuss free.

At a time when the European manufacturers still demanded that riders use a measuring cylinder built into the filler cap of the fuel tank – yes, really – to calculate the oil/gasoline ratio before filling up, Yamaha had fully automatic, and totally reliable, lubrication. Top up the oil tank every 500 miles and ride away: that was it.

Much of this technology was driven by the American market. How important American customers were at the time is sometimes now overlooked, as history is being increasingly re-written. It wasn’t only that there were a lot of potential motorcycle owners in America but the type of customer which the American market presented was radically different from traditional, hardcore motorcyclists. In England, every blue-blooded biker had been brought up with kick starts, manually adjusted ignition and all the associated black arts of coaxing a highly strung motorcycle into life.

In fact, anyone who wasn’t a master of these quasi mystical skills was considered to be rather effete and limp wristed.
The contrast with the USA was stark. American customers wanted, and demanded, in a motorcycle what they had from a car, a washing machine and a fridge. They wanted to use a bike – not treat it like some mechanical deity demanding worship.

It is interesting to note that although the AS1 was designed using Grand Prix technology and European engineering concepts, it was signed off for production neither in Japan nor Yamaha’s European headquarters in Amsterdam. No, the AS1 was going nowhere at all until Yamaha’s Los Angeles Office gave the green light.

If the engine was impressive, then the chassis was just as competent in its own way. Theoretically, the AS engine is a stressed member of the chassis because the frame does not continue beneath the engine. However, with only 15 hp, and a very modest amount of torque, the single spine steel frame is well up to the job.

Since I only ever rode my AS1 flat out, and was one step away from jail in terms of the way I threw it around on public roads, I never found the lightweight front forks and small brakes much of a problem. After all, I expected things to get lively since even a trip to the shops was a re-run of Bill Ivy’s win in the 1966 TT.

The truth is that the bike is under-braked – it uses tiny 110mm (4.3-inch) single, leading shoe brakes front and rear and these did fade badly when hammered. Now, modern brake linings can cure the problem – but not as much as middle-aged owners not riding as if they were in a GP.

This brings us to the AS1C in this test. At the time of launch, America was hovering on the brink of an off-road motorcycling explosion. Forget the rules and regulations of current State Recreational Areas, you could ride almost anywhere there was a bit, or a lot, of dirt without anyone interfering. Truly, they were golden times! So, even street riders wanted a piece of the action and this meant that every manufacturer had a street scrambler.

In the case of the AS1, it meant slightly higher ‘bars, a bash plate and high level exhausts. Otherwise, it was the standard AS1. Even so, the Street Scramblers do hold a peculiar attraction. Chris Bunce, from Classic Super Bikes, who is selling the AS1C, explains. “What makes any bike attractive is always subjective but I do feel that Yamaha got the Street Scrambler version of the AS1 so right that it looks better than the road bike. The balance and lines are just perfect and that is rare on any motorcycle.

“I also like the complete originality of this bike. AS1Cs had a very hard life and were always abused to death. That was the fate of any Street Scrambler. To find an untouched, low 8302 mile example like this one is unicorn horn rare and this is why the price is $6000. Even a fully-restored example wouldn’t be worth this sort of money.”

So, should you own an AS1? The answer is more difficult than it seems. First, you have to find a nice, complete example and this is getting harder year by year. If you strike lucky, and blunder into an AS1 which has been in the back of someone’s garage for the last 40 years then, yes, buy it instantly. There are plenty of engine spares about for these old Yams and the bikes are just as much fun as they ever were to ride. Good luck with the hunt!
MM: Yamaha AS1C 125 Photo Gallery
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wd8cyv   September 2, 2014 03:09 PM
had 1966 ym1 305 cc great bike had it 6 years and over 100,000 miles these bikes were the killers of the english bikes back in the day dave rider since 1953 now use a 2002 MZ RT125 as a daily driver
spyglass   August 29, 2014 04:03 PM
My first scoot was a '68 Yam 180 twin, bought new in the spring of '69. A beautiful little bike, black & chrome and capable of almost 80mph. A change of bar to the street scrambler one and I rode that little beauty 2500 miles in 6mo, nearly all in town and in the enormous Wichita Mts Wildlife Refuge (a great place to ride). That fall, the Kawa KH500 triple was unleashed, and yours truly caught "cc fever"....big mistake. But the little Yam was in the family of the 125 in this article, and all of them were just a blast. Wish I still had it (along with about 4 other ones I shouldn't have traded/sold.....sigh).
AlienVan   August 28, 2014 07:27 AM
Yea what a engine. I put one in a Hodaka frame. Raced it at the Bigbsey Slew on Sunday's. FAST down the straights,BUT,downshift to the corners. The bane of the ROTARY Shifter. There is no stop, goes from 1st to 5th in one click,then you need to go through each gear again to get back to 2nd. The motor sounded just like a bunch of bumble bees with home made exp chambers. And this was the first year of Steen C synthetic lube. So you could wind the engine out with out seizing up. Of course all the steel in the frame was made out of old recycled beer cans. Beer was in steel cans in the old days and you needed a church key to open it. To get strength the Motorcycle frames had to be made thick and hey were heavy.
Drunkula   August 28, 2014 05:23 AM
That's a neat little bike. :-)
spokes   August 27, 2014 08:28 PM
"1968 was the end of the classic era of racing" I remember it well, and people think "the lead footed bureaucrats in the FIM" are something new. The Honda 50cc 4 cylinder, the Honda 250 cc 6 cylinder, the Yamaha 250cc 4 cylinder, etc. Gone but not forgotten. Back in the 80's and 90's didn't all Japanese manufacturers make 4 cylinder 250 bikes? Not two strokes but four strokes, the sound of 18,000 rpm would sound great.
Piglet2010   August 27, 2014 05:58 PM
More than most people want to know about boost ports: http://modelenginenews.org/design/boost_ports.html