Introduction to Yamaha RZ
Few Yamaha series have become as iconic as the Yamaha RZ series of motorcycles. These extremely impressive bikes were one of the best selling Yamaha series in the 80s, thanks to their range of fantastic models.
Designed as a natural evolution of the RD series, the RZ series was sadly banned in the US due to its reliance on two-stroke engines.
When Was The Yamaha RZ Series In Production?
The Yamaha RZ series was first introduced to America in 1980 to advance the extremely popular Yamaha RD series. Its production lasted until 1995, with multiple generations covering the entire series.
One of the main reasons the RZ series stopped being produced was the changes in motorcycle laws across America, especially the exhaust ports emission laws.
Why Is The RZ Series So Significant?
One of the reasons why the RZ series is so important in motorbike history today is that it was the last street-legal two-stroke sold across the US. The ban of two-stroke engines across the US was due to the change in emissions laws.
As these engines produce more power per cycle, their exhaust ports emissions are higher. Most motorcycles switched to using a four-stroke as the emission produced through the exhaust ports are far lower.
Born Out Of The Yamaha RD Series
As the air-cooled RD series became increasingly popular, Yamaha decided an evolution on the famous series was needed. With recent innovations regarding motorcycle construction, Yamaha designed the iconic RZ series.
Yamaha RZ Models
Built around the design of the RZ250 and the RZ350, the RZ50 was a lightweight, super sports model. It featured a lot of what was included in the RZ350 but also featured unique innovations.
The RZ50 made use of the Yamaha Energy Induction System. The YEIS worked perfectly with the single-cylinder engine to produce a 50CC motorbike that maintained a reliable but high level of performance.
Balancing the RZ250 and the RZ50, the RZ125 model featured everything the RZ series was known for, whilst offering an added level of accessibility.
Due to its lower 125CC count, the RZ125 was a perfect option for anyone who craved an RZ without splashing out on a more powerful model.
Reaching the US market in 1980, the RZ250 was one of the first RZ models available to the American public. It had a 247CC engine that featured a two-stroke, parallel-twin cylinder design. The 5-speed gearbox was standard of the time and helped the RZ250 reach its top speed of 157 km/h (98 mp/h)
It quickly cemented itself as a reliable motorbike and was an ideal starting point for anyone interested in owning a Yamaha. The liquid-cooled RZ250 was the equivalent of RD250LC sold in Europe, and especially in the UK.
One of the most popular models, the RZ 350, is still used in vintage racing leagues around the globe. It is so popular that there is a racing competition where the RZ 350 is the only motorbike used, known as the RZ Cups.
The RZ 350 featured a liquid-coolant, 347CC parallel twin-cylinder engine that worked alongside the twin-carburetted reed valve to ensure the highest performance.
The variable exhaust port valve, known as the Yamaha power valve system, was a highlight of this series. It was controlled by a basic computer that helped control the exhaust port timing. This led to high RPM power whilst still maintaining a low RPM torque.
This variant on the RZ350 was produced solely for use in Canada and was commonly referred to as the RD350LC. It was an almost exact copy of the RZ350 except it didn't feature the benchmark YPVS variable exhaust port valve.
First on the market in 1984, the RZ 500 made use of a two-stroke liquid-cooled engine to ensure consistent performance. Its design was based on the famous YZR500 that Kenny Roberts rode during the GP season in 1983.
Unlike similar bike designs, the RZ500 saw a global release comprising of 3 different models per region. These were the RZV500R released in Japan, the RZ500 in Canada, Australia and New Zealand and the RD500LC released across Europe.
Unlike most internal combustion engines, a two-stroke engine can complete a power cycle in two strokes. A two-stroke engine is far more efficient than a typical four-stroke type as it will produce more power per cycle.
They are lighter than most four-stroke engines, however, the added power comes at a cost. They are far more prone to general wear and tear due to their need for higher levels of cooling. All RZ motorcycles made use of two-stroke engines.
As the name might suggest, a liquid-cooled engine maintains low temperatures through the use of a coolant liquid. They are far quieter than an air-cooled system and offer bikes a great way to safely reach higher revs.
The main drawback to a liquid-coolant engine is that it will require more maintenance than an air-cooled variant. The RZ series made use of liquid-cooled engines to provide a quiet ride that maintained high performance.
Yamaha Power Valve System (RZ350)
It was a benchmark for Yamaha bikes of the time and was the only bike in the RD Series that made use of the Yamaha Power valve system. Found in the cylinder exhaust port, the YPVS implemented a spiral-shaped valve that offered variable exhaust timing.
This essentially means the bike could garner more power per RPM as the exhaust port timing would match up with the RPM efficiently.
Racing History: "RZ Cups"
Thanks to its electronically controlled Yamaha power valve system, the RZ350 became an iconic motorcycle in biking history. So much so that even today, regular tournaments are held in Europe and Canada, known as the 'RZ Cups', where all participants ride an RZ350.
How fast is a Yamaha RZ350?
Although it was only a 350CC bike, the Yamaha RZ350 could reach a maximum speed of around 160 km/h (99.5 mp/h). This is incredibly impressive when you consider that this was a 350CC bike made in the 80s.
What is the Yamaha Power Valve System?
The YPVS was an electronically controlled variable height exhaust port system that used a basic computer to offer a range of exhaust timings. This helped the RZ350 bike, the only RZ bike to use it, maintain regular RPM power across the board.