(first posted 9/16/2012) I doubt that it’s possible to overstate the degree to which the world changed during the 1960s. Indisputably, it was a decade of innovation and change in many areas besides motorcycling. But as surely as history was being rewritten in Saigon and Woodstock, so changed the look, feel and performance of motorcycles.
According to Yamaha market research, there was vast and untapped market for dual-purpose off-road bikes. Sure, people had been removing lights and making upswept pipes and homemade skid plates for years, but now Yamaha would do it all at the factory, on a mass scale unlike the little specialty off-roaders. The Yamaha DT-1 (above) arrived in 1968, and the first run of 12,000 bikes sold out immediately. Yamaha had a runaway hit on its hands, and soon there was a full family of DTs.
It’s likely that there will never be one bike that satisfies everyone’s needs. For those going off road, weight and size are the enemy. What’s more, while a two-stroke single engine will handle most street duties, it’s not meant to go cross-country or interstate, only across town. Some contemporary British bikes were capable on both streets and highways, but they were pretty heavy. Ride to the dirt–no need for a truck to tote the bike. Why did no manufacturer before Yamaha recognize that? Beats me. They were breaking new ground when everyone else was playing catch up.
On the other end of the spectrum were trails-oriented bikes like the brilliant Bultaco Sherpa T, which made all the old English four-stroke thumpers obsolete. But you wouldn’t likely consider riding this down the road for any length. What America needed was an affordable dual-purpose bike, and Yamaha gave it to them, in spades.
I guess one could gather that Yamaha was full of bright people who knew what the American buying public wanted. That would make a good story, but in truth, Yamaha was full of bright people who knew how to ask questions. Plenty of desert (and other) racers were more than happy to give them some good answers. But before we look at the different models in the Yamaha DT lineup, let’s review what’s essential to a good dual-purpose bike.
First, dual-purpose tires: My first on- or off-road tires, Bridgestones, had a more aggressive tread than street tires. They looked a lot like this, and actually put a lot of rubber to the road surface.
I recall the time I hit an oil slick on the road that moved me across a full lane of traffic. If I’d been using dedicated off-road knobbies like these, I probably wouldn’t be writing this story. I feel lucky as it is. A number of people who fitted them for off-roading were shocked to discover that they turn pavement into something very slippery.
Obviously, an off-road bike needs more ground clearance than a street bike. On the street, the extra clearance simply increases wind resistance, which becomes a factor when you’re move out. On the other hand, if you take a street bike off road, you’ll likely be leaving (1) the exhaust pipes on a rock somewhere, or (2) your bike at the spot where it is. I’d say that this bike’s problems stemmed from its tires and weight. Of course, some terrain just isn’t bikeable. Really porky adventure bikes can literally provide you with an adventure.
I’m not an engineer, which makes explaining these engine types a bit difficult. Let’s just say that the two-stroke single is narrower and lighter than a comparable four stroke. Moreover, a single gives you better traction in the dirt; each interrupted power pulse gives the wheel a chance to dig in. Power isn’t the only reason large, multiple-cylinder engines were banned from dirt track: They tend to spin, and not dig in.
The DT-1 was a 250, with 23 hp and a wide powerband, perfect for the type of use it was expected to see: more on-road than of-road, but capable in either one.
This little jewel is identical to the bike I rode all over the Panamanian rain forest. A DT250 was certainly heavier and less powerful than such professional off-road bikes as Bultacos and Husqvarnas. It costs money to make high quality light bikes, but after you took the time to strip one of these, you had something that would do quite well. It was fairly light for the price, and powerful enough to keep up with traffic, on or off the road. With the 250, Yamaha hit a home run. I owned one and loved it, but I’m still not certain it was their best bike.
Yamaha knew that buyers in the U.S. were already comfortable with four-strokes, and that they didn’t particularly like mixing oil and gas. Their answer was automatic lubing system, called Yamalube, whose only visible component was a small glass circle at the bottom left of the oil tank. If you couldn’t see oil in it, catastrophe was imminent. Just fill it and forget about it, at least for several tankfuls of gas.
A pulsating air system gave the Yamahas a power advantage over other two-stroke engines. In a normal two-stroke system, the piston tries to push air back through the intake port. This reed valve is a one-way system that stops that problem. You are viewing it from the engine side.
The Yamaha exhaust system contained elements of an expansion-chamber system which, when combined with the reed valve, made the engine far more efficient: Exhaust gas exiting the engine is allowed to expand before being constricted just before it leaves the pipe. That sends a power pulse back to the engine that, with correct timing, pushes fresh gas and air back into the cylinder instead of letting it escape. It’s not the full expansion chamber associated with motocross bikes; after all, that would create licensing problems. In addition, these bikes were fitted with muffling and a spark arrestor to comply with local laws.
I can’t get enough of this little animated graphic of a two-stroke, so here it is again; maybe not for the last time.
Long travel suspension is absolutely necessary for going fast off-road, but is not good for street bikes for many reasons. Looking at the top bike, you can see how its fork and rear shock are extended; the travel on a modern dirt bike would be longer. Thus, Yamaha compromised. I felt very comfortable at 60 mph, and slightly less so trying to go fast in the dirt.
Early in the DT’s evolution, Yamaha decide to adapt existing motocross frames for use on the next year’s DTs. Better in the dirt. Not so on the road.
The DT-1 was a mammoth success, and soon was selling at some 50,000 per year, almost unheard of. Yamaha instantly knew it had struck gold, and a whole family of DTs soon arrived; everything from 50cc to 400cc. Yamaha’s DTs re-defined the bike market, and had an unbelievable impact on the market. Dual purpose bikes were cool, until the fad (like all) petered out.
There are still some out there if you look. Just yesterday I stumbled across a DT175, bought by a friend who is in the process of repairing it. After only 4,000 miles the spark died, so he’s busy installing a 12v system from a Honda ATV. I would be lost in there, but he isn’t–and he’s looking forward to having fun.
I truly lusted for the Bultaco Sherpa Ts and Alpinas. But they cost almost as much as a new car. I bought the new car.
I used to have (sold it on e-bay) the factory service manual for this bike, and in the supplement in the back, they had a factory hop-up kit available, with ported cylinder, high compression head, and new pipe, and was good for 32Hp.
A lot of my friends had the 80 and 100 versions of this bike, my Honda XL-75 couldn’t keep up with them, but I never burned out the motor by forgetting to check the Yamalube port either. That 4 stroke bike was like a Timex, it just kept going and going. I wish I could still buy one (or one of these) new today.
Mate o mine had a RT 360 made for 6 months before the DT arrived tough old bike but the whole transmission had to have the gears n dogs built up with stellite and reground and you needed to be wary of the ankle breaking kickstart brilliant on trails plenty of grunt.
That is one of the most beautiful “enduro” bikes produced. I’ve been thinking more and more about them but lately I’ve been itching to find a 79 Maico GS 501 or 73 250MX.
I didn’t get into Yamaha until the water cooled 82 YZ 250 came out. I buried that bike a few times in the same way that the expedition bike up there was, luckily Illinois farmland isn’t quite so desolate.
There were a couple of reasons why the British never really twigged on to coming up with a bike like the DT-1:
1. British singles were what was loving called at the time ‘grey porridge’. Boring, overly heavy street singles used for daily transportation by people who were rich enough to put the 3-speed bicycle away in the shed, but still couldn’t afford a car. They were moderate performance, high fuel mileage, comfortable bikes with very little sporting instinct – the kind of bike that people ask today “why can’t the manufacturers make . . . . . ?” The fact that they failed completely once the Mini came out is why the manufacturers can’t. People either want sport on a budget, or the comfort of a sedan. They don’t want the performance of a sedan and all the bad weather protection of a two-wheeled road burner.
2. Villiers. In the 1950’s, Villiers took over the British two-stroke market (with the exception of the BSA Bantam and the Ariel Leader). For their day (early to mid-50’s), they made the best two-strokes available, and every manfacturer used them (just like they all used Lucas electrics, Lucas instruments, Girling shocks, etc.) Unfortunately, just like the rest of the industry, Villiers figured they had it made and never bothered improving their product. To the very end, you mixed oil in the gas tank. Oil injection? Needless frippery. So no other manufacturer had any incentive to try and improve the two-stoke based on what the East Germans and later Suzuki were doing.
Put the above two lines of thought together, and it’s easy to see where the concept of a light four stroke single, or oil-injected two stroke with torque and power just never occurred to the British. It wasn’t the way they did things.
For a number of years, I had the DT-1’s predecessor: A Yamaha (can’t remember the model name, C3-SC?) 100cc street scrambler, a two cylinder two-stroke with high pipes on essentially a street chassis with a bash plates and knobbies on spoked steel rims. It handled pathetically as a street bike (I almost killed myself the first time I took it thru a set of twisties, having ridden almost totally Triumphs up to the point), and had damned little suspension travel off-road.
As a kid growing up in Vancouver Island in the mid-1970s, I saw just loads of DTs around. They were cheap, easy to maintain, capable of the highway or any logging road and fun to ride. I have had many friends have various DTs, usually the 250. I have ridden a few and they are really high quality pieces. Bikes this good made the entire bike industry way better.
If it weren’t for this bike I doubt that Honda would have made the SL175 I mentioned last week. For my money I think the DT175 gave the best bang for the buck. Lighter and almost as much horsepower (higher rpm) and cheaper. If I had been buying a new one I think that’s where I would have gone. Got the DT250 second hand and cheap. No regrets.
i think I had a DT 125, CT 90 and another 125 road bike.
Which was fun to ride on the dirt rd and back yard.
The Yamaha bikes from 1968 to the early ’70s had remarkable style and the engineering coming out of Japan was top notch — no oil leaks, for example, as was common with British bikes and the AMF-owned Harley-Davidson Co. My family has only had Yamaha and Honda motorcycles.
As a side note to Lee Wilcox: How could you allude to the 1960s and not mention men walking on the moon?
I have no excuse for forgetting the man walking on the moon. I was a member of the Navy Unit that decontaminated him and his stuff (Ft Detrick Md.). Thinking of it that way makes it inexcusable.
Btw, the DT175 I mentioned at the end of the paragraph is mine now. Haven’t ridden it much but I intend to.
My 1st motorcycle was almost a near new Yamaha XT250…or 500, it’s been nearly 35 years. Instead, I went entirely the other way and bought a new XJ650 (a Seca). Then, when some nitwit pulled into my path and I totalled the Seca, I considered replacing it with a dual sport bike but couldn’t make up my mind as to brand and displacement.
I had a F11 250 Kawasaki 1973 same recipe as this light two stroke single that would rev way past the marked redline it was only let down by the date suspension, not enough travel great little bike though.
Back when everybody started riding lawnmower powered minibikes and moved up from there. Every vacant lot had kids riding on them until somebody sued the owner and then the elitists banned off-road motorcycles from just about everywhere while still allowing their wealthy equestrian buddies access. Working class people have been cut off from their cheap fun. Yamaha and all the cheap dual purpose motorcycles were the gateway drug to a world of dirt bikes I still cherish at 60 yrs old but what of the youth today?
That Yamaha with the orange tank made me lust for that bike. Even today, when looking at it does something magical to me.
I never forgot looking at the Yamaha ad that was pictured in the desert all their models. I practically wore out the pages with my eyes.
I had a Yamaha GT80 in high school before I got my driver’s license, but I always wanted to upgrade to a DT100. Which begs the question, were any Yamaha Enduro bikes ever fitted with the Monoshock system that premiered on the YZ Motocross bikes? My dream bike is still a DT100, fitted with a Monoshock system!
The DT80 came with monoshock & twin meters in the late 70’s. Wonderful little monster! Ran & kept up with Z250(Kavasaki) GS250(Suzuki) CS250(Yamaha) & CB250, CB250N(Honda) all 4strkers. Broke a “slight” sweat on the road running with the bigger bikes but always kept up
Yep ;
These were real game changers .
Up to 1967 Yamaha had been experimenting with heavy electric start two strokers, they were okay, not great at anything but sturdy and well built .
My high school buddy had his father’s 1967 YL2-C, a 100C.C. single with electric start (a dynamotor of all things) and he couldn’t kill it ~ we’d go off riding and when it began to bind up from lack of oil in the tank we’d go by a gas station and beg some drain oil….
In the late 1970’s I had a DT175 and when I was skinny (185 #) it was a fine bike to ride, I never took it off road but it handled the Los Angeles area freeways just fine .
The Japanese were smarter than the American bike manufacturers, : they listened to what the buyers wanted .
-Nate
Interesting article and informative. I have read many times about the importance of the exhaust on a two stroke but that cute graphic really shows it to perfection. The only comments I would make is the traction due to “power pulses” does not add up. Time to dig in does not apply At 6000 rpm on a 2 stroke that 100 power pulses per sec or one every 0.01 second. Which btw is the same for a 2 cylinder 4 stroke (if sequential fire). Otherwise great article especially interesting about the decontamination coment!
When I was all off 11 years old and my brother was 10, we begged our life-long motorcycle enthusiast Father to buy us a Briggs & Stratton lawnmower engine based “mini-bike” from the Sears, Roebuck & Co catalog.
Dad vehemently refused, mentioning the tiny tires, short wheelbase and inadequate rear wheel only brake. He called it a “Shi**y handling POS death trap”; unfit for his children to get hurt or killed on.
Instead, Dad brought us home this Yamaha Mini-Enduro. We were properly delighted and became the envy of our suburban tract home neighborhood.
A few years later Dad bought us the subject of this entry. Once again, we became the objects of neighborhood envy.
Quite the extravagant gifts from our unusually “Great Depression Baby” Frugal Father!
My dad bought me a 1972 125 enduro with torche induction.. best ever! Unless you got the bigger ones! Also was prilaged to ride my friends Yamaha mx100. That thing was fast! Of course at the time and age.