Here we take a look back at the glory years for both road going 2 stroke bikes and MotoGP racers plus a dive into the 2 stroke engine, warts and all to discover why it was doomed once emissions became an issue.
Let’s get to it.
History of the two stroke motorcycle
Alfred Angas Scott of Yorkshire created the initial workable two-stroke engine. The original two-stroke motorcycle engine design was then patented in 1904 by Scott Motorcycles, with twin-cylinder, water-cooled motorcycles being the first vehicle the business produced shortly after in 1908.
Within 4 years the Scott 2 stroke bikes were regularly the fastest at the Isle of Man TT with wins in both 1912 and 1913.
In the decades that followed, two-stroke motorcycles gained in popularity but didn’t reach large scale manufacturing until the 1960s and 1970s when the Japanese motorcycle industry started to see the benefits.
The straightforward two-stroke engine was built more quickly and cheaply thanks to more modern technologies and so the era of the two strokes began.
Over time, the primary flaw of this fundamental design—their fuel thirst—became clear. The fuel consumption was making them expensive to run with the increased cost of oil and their emissions proving harmful to the environment, this proved to be their downfall.
Six of the Greatest 20th Century Two Stroke Motorcycles
The Japanese motorcycle manufacturers were dominant during the late 60’s through to the 80’s, during the “golden age” of the two-strokers.
During this time Suzuki, Kawasaki and Yamaha would go on to produce what many would arguably call their greatest machines, with Honda sticking to their mantra about being a four-stroke manufacturer up until the 80’s, where despite arriving late to the party, created some amazing machines.
Kawasaki H2 Mach VI
Known as the Widow Maker, the Kawasaki H2 750 Mach VI was a direct result of the success of the 500 cc Kawasaki H1 Mach III introduced in 1969. The 748 cc 3-cylinder was one of the most uncompromising motorcycles ever produced, producing 74 bhp (55 kW), cutting a 1/4-mile time of 11.95 seconds at 115 mph — a production-bike record in 1972. Unlike the H1 500, the 750 had much more low engine speed torque, with a strong burst of power starting at 3,500 rpm to the 7,500 rpm red line.
Not only was the H2 a fitting replacement to the world-beating 500cc H1, but it was also Kawasaki’s response to the newly launched first superbike, the Honda CB750.
The Suzuki GT750 was built from the Suzuki T500 with an additional cylinder and liquid cooling. The GT750 had a 739 cc three-cylinder engine and weighed in at 250 kg. It had a five-speed transmission, and a three-to-four exhaust system.
The prototype Suzuki GT750 was displayed at the 17th Tokyo Motor Show in October 1970 as a response to Honda’s ground-breaking CB750, and released in Japan in September 1971 as a sports tourer (GT standing for Grand Tourismo).
It’s liquid-cooled engine was significant as it was the first production bike to be liquid-cooled since the Scott two-strokes in the 20’s and 30’s. As a result, the GT750 quickly adopted several nicknames globally pertaining to its water-cooled engine, including “Water Bottle” in Australia, “Kettle” in Britain, and “Water Buffalo” in the US.
Suzuki RG250 Gamma
From 1983 to 1987, Suzuki developed the 250cc two-stroke Suzuki RG250 Gamma, which had a water-cooled parallel twin engine. The RG250 Gamma’s amazing power to weight ratio was one of its standout features; weighing in at 130 kg and producing up to 45 bhp and 38.4 Nm of torque.
The RG250 Gamma was the first mass-produced motorbike with an aluminium frame that was lightweight with an aerodynamic fairing similar to those used in racing, kicking off a trend amongst the manufacturers. All this meant a top speed of 107 mph (172 kph).
The initial Mk1 models of the Gamma had a very sophisticated “Full Floater” suspension system for its time alongside “anti-dive” front forks (which locked the front forks under hard braking to stop them diving). The Gamma became known as the first street legal racer because of how quickly and effectively it handled.
In 1987, the V-twin engine RGV250 finally took its place.
Yamaha produced some of the best 2 strokes we’ve ever had and several of those were “over-the-counter” racers of various capacities throughout the 1970s and 1980s. Its crowning achievement is the TZ750 which tops them all.
A development of the TZ700 it was built by Yamaha to compete in the Formula 750 class and became the go-to track bike for privateers.
It won countless Formula 750 races and championships, open class races, won Daytona 200 nine times in-a-row and was the bike that Joey Dunlop rode to victory in the 1980 Classic TT during the process of which he upped the lap record on the Snaefell Mountain Course to an average speed of 115.22 mph. This is also the fastest recorded lap of the Mountain Course by a Yamaha 750cc two-stroke machine.
US magazine Motor Cyclist called the Yamaha TZ750 “the most notorious and successful racing motorcycle of the 1970s”.
In 1971, the UK passed a law limiting the size of mopeds that 16-year-olds could ride to those with pedals and engines under 50 cc.
Yamaha saw an opportunity and in 1973 introduced the FS1-E with pedals attached to comply with UK regulations. This became every young motorcyclist’s ticket to freedom.
Simply put, the “E” suffix at the end of the model name indicated which country’s rules the FS1 had been designed to satisfy. “E” was for England.
The bike’s engine was a 49cc, single-cylinder, two-stroke, air-cooled motor with rotary disc valves and a four-speed transmission as compared to the five-speed in the original FS1.
The Yamaha FS1-E, known among British youngsters as the “Fizzie,” rapidly became for many people their introduction to life on two wheels. For the UK market, almost 200,000 units were earning it a solid place in British motorcycling history and in the hearts of an entire generation of bikers.
The original NSR250R MC16 was Honda’s attempt to compete with Yamaha’s newly released TZR250, and at the time, its unique 3-spoke alloy wheels, heavy duty box-section frame and swingarm, and racy design made the TZR look rather conventional.
It developed from the well-known NS250R MC11 and was built across four different versions, each powered with 249cc 90° V-twin two-stroke liquid-cooled engines. All engines used the Honda RC-Valve power valve system and cylinder bores coated with nikasil-sulfur (thus the “NS” in “NSR”).
Due to Japan’s licence regulations, it produced the same amount of power as the MC11 but weighed around 20 kg lighter and used the revolutionary new RC Valve variable height exhaust power valve system, making it an incredibly quick but flexible bike for its time.
Even though it was always a JDM (Japanese Domestic Market) bike, the motor once delimited was actually capable of producing 55 bhp, easily putting it on par with the RG250, KR250, and TZR250, and in full racing TT-Formula 3 trim, was capable of over 70 bhp.
The Honda NSR250 design was straight from Freddie Spencer’s championship winning bike, although they shared no mechanical parts.
For many more detailed two stroke smoker reviews check out our complete section HERE
4 stroke motorcycles dominated the 500cc class of motorcycle racing up to the beginning of the 1970s. Technically speaking, it was believed to be impossible to ever produce a trustworthy 500cc two-stroke racer. Along with British frame builder Colin Seeley, Barry Sheene was the one who forever altered that perspective.
Barry’s father, Franco, took the air-cooled twin engine from a fast but terrible handling factory TR500 Suzuki and sent it to Seeley to build a motorcycle that handled as well as vintage Matchless and Norton singles but could compete with the two-stroke Kawasaki triples that were beginning to show up in Grand Prix racing.
Seeley was successful, and the new machine demonstrated that Sheene could ride large bikes in the Premier class of motorcycle racing just as effectively as he did the 125s on which he became famous.
As good as the Suzuki TR500 engine was, and the greatest engines at the end of its lifespan produced over 70 horsepower, it was always a road engine that was never designed for racing. A real, purpose built GP bike was required.
The first major manufacturer to enter the competition to build a large two-stroke racer was Yamaha. They created a 500cc, four-cylinder bike in 1975 that GP icon Giacomo Agostini used to win his final World Championship using their knowledge of 250 cc twin cylinder races.
Suzuki, in comparison, began from scratch and created a square-shaped, four-cylinder disc valved engine. The factory had knowledge with this design thanks to their 250cc GP bike; this new “Square Four” went on to become the illustrious RG500 and helped Sheene win two World Championships in 1976 and 1977.
With a slew of new models that kept getting better and with the incredibly skilled Kenny Roberts on board, Yamaha answered back and retook the mantle from Suzuki, winning the championship in 1978, 1979, and 1980.
Honda was at the time, adamant that they were a 4 stroke only manufacturer. They had been responsible for creating the storied five-cylinder 125 cc and six-cylinder 250 cc motorcycles that dominated GPs in the 1960s and were sticking to their guns.
It wasn’t until 1982 that Honda finally acknowledged the truth of the matter and began producing their own 2 stroke motorcycles.
As a consequence, the NS 500 triple, which featured two vertical and one horizontal cylinder, was created. The Honda was simple to ride and had excellent handling despite having less horsepower than the Suzuki and Yamaha. With the help of this bike, Freddie Spencer won two world championships.
Despite how effective the triple was, it could never match a V4, which was the ultimate weapon in the 2 stroke conflict. Honda and Yamaha fought it out with bikes that generated incredible amounts of power for such little weight during the 1980s. This layout delivered the finest possible mix of handling and power.
However, it was Honda, their V4, and Mick Doohan who controlled the late 1990s with five straight wins. Suzuki were still in the battle, and Kevin Schwantz managed to win the 1993 title on his RGV.
Suzuki continued to fight back with another RGV upgrade. In 2000, Kenny Roberts Junior triumphed on the Suzuki against the young, rising Valentino Rossi, who had recently switched to the 500cc class.
When Rossi discovered out how to race the NSR, the young Italian dominated the field until the 4 stroke 990 cc MotoGP bike was introduced in 2002 spelling the end of the 2 stroke era in the motorcycling racing premier class.
The two-stroke engine
A two stroke engine is a reciprocating engine that only requires two piston strokes to complete a power cycle. The crankshaft of the engine completes one rotation after two piston strokes:
- The piston’s first stroke completes the intake and compression operations.
- The second piston stroke marks the end of the power and exhaust processes.
The thermal efficiency of a two-stroke engine depends on the design. In general, a petrol engine only converts 20% of the fuel into mechanical power.
75% of this energy is utilised to power the wheels, with the remaining 25% being lost as heat from friction and other sources.
In contrast to 4 stroke engines, scavenging ports in the cylinder wall are employed to draw in air and release exhaust instead of using intake and exhaust valves.
2 stroke motors have more power output than their 4 stroke equivalents, which finish their power cycle after four piston strokes or two crankshaft rotations. Since 4-stroke motors contain more components, they are also heavier and are more expensive to produce. The 2 strokes, on the other hand, are less adaptable and need a lot more oil.
At the peak of the golden era of 2 stroke road bikes in the 1970s, models like the Kawasaki H2 were making any 4 stroke competitor appear slow and encumbered. However, the end of this era was approaching with governments looking strongly at vehicle emission and greenhouse gasses that were polluting the atmosphere.
The fact that you could see the emissions leaving a 2 stroke vehicle’s tailpipe didn’t sit well with the environmental movement; simply put, engine technology needed to improve quickly.
It was quite simple to adjust 4 stroke motors for improved emissions since they used valves, cams, and timing mechanisms.
The less fuel-hungry 4 stroke motor was more economically viable for manufacturers to invest in during the 1970s and 1980s era of more stringent EPA rules than it was to spend years and millions of dollars in research and development on how to make a two-stroke engine accomplish the same feat.
Major manufacturers soon shifted to four-stroke engines for motorcycles and passenger vehicles all over the world, and in the USA, the sale of all two stroke vehicles was banned in 1984 since they couldn’t be retrofitted to meet road regulations for emissions reduction.
The UK followed suit in 2004 when two-stroke engines were relegated for use with low cc scooters only. Manufacturers all but ditched the format following the ban in America and two-strokes were resigned to history. Mostly.
Modern Era 2 stroke motorcycles
KTM was almost singlehandedly responsible for preserving the good name of 2 stroke dirt bikes through the 2000s and 2010s. As the big factories like Honda started abandoning this technology, KTM doubled down by offering a full range of off-road 2 strokes for riders of any experience level. These days over half of KTM’s annual sales are 2 strokes, this gives a great indication of the market and want of 2 stroke bikes.
In 2018, KTM announced transfer port fuel injection, a technology that ditches the carburetor in favour of precise control over air-fuel mixtures and emissions, potentially leading to a new era of street legal 2 stroke engines in a future.
Yamaha have very recently been re-investing back into their two-stroke engine dirt bike offerings. Most notably their 2022 YZ125 with a long list of changes that have been implemented: from the 125cc two-stroke engine’s internals, a revised transmission, Keihin carburetor, updated KYB suspension and new bodywork
Outside of the off-road scene the large manufacturers are sticking with the four-stroke formula after decades of R&D and now look to electric as the inevitable replacement of the combustion engine as a whole.
For those who are looking for something special, the ol’ 2 stroke thunder without the death clause there are a few smaller, more specialised manufacturers making new street legal two-stokes to modern specifications.
Heading the current charge is the UK-based firm Langen who have created a brand new 250 cc 2-stroke putting out 76 bhp that meets all current emission rules.
There’s also a Swiss outfit producing their Suter MMX500 and a German team who produced the Ronax 500, a V-four, two stroke GP race replica based loosely on the track bike Yamaha YZR500 which in turn led to the (barely) road legal RD500LC.
All 3 of these were built to a limited run (with some availability left should you be looking) and while the Langen 250 Two Stroke costs a reasonable £33K the other 2 offerings start at 6 figures.