1975 Yamaha RD350B
Claimed power: 39hp @ 7,500rpm
Top speed: 95mph (period test)
Engine: 347cc air-cooled 2-stroke parallel twin, 64mm x 54mm bore and stroke, 6.6:1 compression ratio
Weight (wet): 352lb (160kg)
Fuel capacity/MPG: 3.2 gal (12ltr)/35-40mpg
Price then/now: $1,224 (1975)/$1,500-$4,000
School is out and the cool kids, the ones with the feathered rocker hair, Led Zeppelin T-shirts and worn jeans, are headed for the parking lot. Two swift kicks and a Yamaha RD350 chatters into life.
That ring-ding-ding sound is unmistakable as the helmetless owner threads his way through the after-school traffic, narrowly missing a mother driving her daughter home. Mother is appalled. Daughter smiles. She is thinking about sneaking out of the house to meet that insolent creature on his bad boy bike.
The RD350 was THE Seventies poor boy racer. It was relatively cheap, relatively easy to work on and fast through the twisties. Unlike the many stoplight-to-stoplight dragsters of the early Seventies that had to be muscled through corners, the RD was light and flickable, just the thing an aspiring racer needed to hone cornering skills. “It was brutal, fast and wheelie prone,” says Zeki Abed, the proud owner of the original-condition RD in the Image Gallery.
Unfortunately, teenage racers are not the best at caring for their toys. Although a best-seller in the mid-Seventies, finding a Yamaha RD350 in good shape today isn’t easy. The RDs that weren’t thrown away in Turn 7 or slid out on a patch of gravel on a mountain road were still usually ridden hard and often put away wet, the maintenance schedule forgotten.
Our feature RD is one of the few lucky ones. Mostly original and in excellent running shape, it was bought new by an engineer, who kept it until just a year ago when he sold it to classic Japanese motorcycle collector Zeki, who treasures it because it makes him feel like a kid again — a bad kid. “It’s the bike I never had,” Zeki says. “It’s the bike that would blow away everything up to a 750.”
Although Yamaha is now the second largest motorcycle manufacturer in the world, in the early 1960s it was just one of a group of Japanese manufacturers struggling to catch Honda, the industry leader. In 1962 Yamaha introduced the YD3, a 250cc sporting 2-stroke twin with electric start. A successful export, it encouraged Yamaha to concentrate on 2-strokes, with an eye toward aspiring club racers.
Although 2-strokes had a power advantage over their 4-stroke brethren, they did have a major drawback, and that was the need to mix oil with the gas, an inconvenient and sometimes messy chore. In 1964, Yamaha introduced the Autolube system, which pumped oil from a tank to mix with the gas going into the crankcase. It was an innovation others would follow.
In 1967, Yamaha followed the YD3 with the YDS5, a completely redesigned and updated 250, and the YR1, a 350cc 2-stroke twin. Both of these bikes were geared towards sporty performance, and a production racing version of the YDS5, the TD1C, proved a winner on the track and was joined two years later by the 350cc TR2. Word got around that these Yamaha racers could be uncrated and pushed directly onto the starting line, no expensive setup required. Better yet, the Yamaha racers often beat much bigger machines. Aspiring café racers and track racers alike felt that Yamaha was responsive to their needs, and as a result they went out and bought Yamaha road bikes. When Yamaha came out with the light and reliable DT1 250cc trail bike in 1968, offroad enthusiasts were added to the crowd of Yamaha boosters. By the late 1960s, Yamaha was selling enough bikes to challenge Honda for leadership of the Japanese motorcycle industry.
Armed with feedback from the production racing crowd, Yamaha engineers updated the YR1, improving the styling for good measure. The result was the 35 horsepower R5, which appeared in 1970 and was even more successful than the YR1. But the best was yet to come. The RD350, which started hitting showrooms in early 1973, was the next step up.
This 347cc twin took a lot of its basic design from the Yamaha production racers, including the double cradle frame and the 2-stroke engine. As Cycle magazine said, “It has a racing connection deeper than advertising copy.” It showcased two major upgrades over prior Yamahas: A reed valve induction system and a front disc brake.
Unlike 4-stroke valves, reed valves are inserts in the intake tract of 2-stroke engines that allow gas and air to flow one way only. A 2-stoke engine compresses the fuel/air mix in the crankcase. With a simple piston-port engine, mix can leak back (“blow back”) into the carburetors. With the addition of reed valves, fuel mix can’t back out, improving cylinder filling.
The RD also featured an additional port in the induction system. When each of the RD’s pistons neared the bottom of their stroke, they uncovered a small port fed directly from the carburetor manifold. At the same time that the preheated compressed mix entered the combustion chamber from the crankcase, an extra, small shot of fuel and air was inducted. Yamaha literature claimed that this improved combustion chamber filling and scavenging, and cooled the piston crown.
As a result of Yamaha’s “Torque Induction” system — along with a crankshaft supported by large ball bearings, with roller bearings at the bottom and needle bearings at the top of the connecting rods and a 6-speed transmission — the RD pulled well from 4,500rpm to 6,500rpm, made 39 horsepower, and topped out just shy of 100mph. Not bad for a 350. The reed valve system also improved gas consumption, a constant problem for Seventies 2-strokes. Period tests varied between 35 and 40mpg.
Power, in order to be usable, especially rounding a curve, must be transmitted to the ground in an organized way. Here, the Yamaha had the benefit of a stiff frame with additional bracing, and gussets around the swingarm and steering head. Contemporary testers were impressed with the RD’s stability and ability to change course through a turn when asked.
Power must also be controllable. Although Honda pioneered disc brakes on production motorcycles, period testers described the Yamaha front brake as one of the best on offer, with a master cylinder operating two 1.75-inch pucks on a 10.5-inch disc. Cycle liked the setup enough to claim “the little 350 generates enough decelerative force to jerk your eyeballs out.” The Yamaha RD350 took 122 feet to stop from 60mph — not really exceptional by today’s standards, but in 1973, the act of making a motorcycle stop well was relatively new; no gorilla grip needed — the brakes on the RD were responsive even under light pressure.
Like most 2-strokes, the RD needed revs to perform, but gearshifts were quick and easy, making shifting anything but a chore. Testers did have some minor quibbles, however. Everyone thought the paint scheme (red with a broad white stripe) was gaudy, the front wheel had a tendency to become airborne under hard acceleration, the seat was uncomfortable after a few miles, and the oil tank leaked.
Tester’s quibbles didn’t faze the cool kids who bought Yamaha RD350s. Many worked on their bikes, adding performance upgrades well-known among enthusiasts. “It’s easily modified,” Zeki explains. “Rejet the Mikuni carburetors, put on K&N air filters, upgrade the shocks, add a front fork brace, steering damper, expansion chambers and low bars. Remove the centerstand. You can also install DG Radial heads for better cooling and increased performance. You will blow anything up to a 750 into the weeds around town or on the back roads.”
With a bike this right, Yamaha wisely left it mostly alone in later model years. The paint scheme changed (solid red with two thin horizontal white stripes for 1974, orange with black stripes as on our feature bike in 1975; testers didn’t like them, either), the intake tract was revised in an effort to lower the noise level, and an O-ring was added to the crank near the primary gear to stop an oil leak. For some reason, a 1975 Cycle World test found the brakes were less responsive than the first bike it tested in 1973: it now took 132 feet to stop from 60mph.
Yamaha introduced the 400cc RD400 in 1976, with more horsepower and a thicker and more comfy seat. More weight forwards damped the 350’s tendency to wheelie. However, increasingly stringent EPA regulations ended the market for street legal air-cooled 2-strokes in 1980.
Meanwhile, the cool kids grew up — or maybe they mostly grew up. Somewhere in the corner of a mind, the need for speed hibernated, waiting for the right time to blossom forth again. For many, it was finding themselves with an empty nest and some disposable income after years of hard work. The once-cool kids started gravitating to vintage bike races and clubs.
As early as 1991, Cycle World predicted the RD350’s status as a future collectible. Japanese motorcycle enthusiasts were already snapping up bikes with minor issues for a song. After searching for the right RD for years, Zeki located this original gem a year ago. Once Zeki convinced its engineer owner to part with his RD, Zeki took it home and checked it over — and found there was very little wrong that would not respond to a damp rag and some polish. “It was beautiful and pristine, in stock condition and unmolested. It had some slight pitting on the spokes and I had to clean the film off the mirrors. That was it,” Zeki says.
Zeki has about 20 bikes, but this is one he rides frequently. The RD is kickstart only, but starting is simple: Turn on the ignition, put the choke lever on and kick — no more than two kicks, even if it is cold. Then you have to wait a couple of minutes for the little beast to warm up. Zeki says the RD will bump start easily if the battery is dead: “Just roll it down a small slope or get a running start, jump on it and drop it into first.”
The oil injection works in conjunction with the throttle, so it’s best to keep the RD moving. It can get hot if stuck in traffic. “Canyon riding is its realm,” Zeki says. “The clutch is light, shifting is light. It’s a very responsive bike. It flicks to right and left and is very forgiving for a bike of its era.”
The Yamaha RD350 had a reputation in the Seventies of being low maintenance, and Zeki reports he has had to do very little to his. “A lot of people take out the oil injection, but I have never had an oil injector fail. I think it is more of a racing issue. Every 3,500 miles I take it to my mechanic, Bob Davis in Santa Cruz, and he checks the carbs and points, changes the condenser and puts in new spark plugs.”
Zeki is emphatic about the continuing appeal of the RD. “In my mind, pound for pound, dollar for dollar, the RD gives you the best bang for the buck of any bike built between 1973 and 20 years since. It will give great satisfaction to any rider. It will put a smile on your face.” MC
“It offers a combination of two winning features: devastating performance and excitement at a moderate price, and the seemingly contradictory promise of appliance-like reliability.”
— Cycle World, February 1973
“The bike can burn through switchbacks and carve around sweepers like few in its displacement class and few in any other class. It is easy to start, consumes fuel, oil and spark plugs in moderation, can go over 100mph, stops harder than any production motorcycle in captivity, can countenance highway trips without inflicting pain, and is easily serviced.”
— Cycle, May 1973
“The RD350 is in a class by itself. It will comfortably wax all bikes with equal displacement and will out-brake any machine in motorcycling. Keep the 6-speed box in harmony with the power band and the Yamaha will climb mountains as fast as you can ride.”
— Cycle, February 1974
“Persistent development and an honest-to-God race pedigree have yielded a motorcycle that is as splendid as it is specialized. An expert’s motorcycle in every sense of the word, it is a superbike — that simply happens to be short.”
— Cycle, December 1974
“The Yamaha RD350B is one of our favorite motorcycles. … Its engine will perform comfortably around town, yet can thrill you at the racetrack while embarrassing riders on some bigger bikes.”
— Cycle Guide, March 1975
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