Vintage Hall: Yamaha RD350B

The RD350B was a two-banger that rolled out of Yamaha’s factory in 1975 hailed as a a race-bred motorcycle in street machine clothing.

Blue Smoke in Top Gear

Though Phil Read won the 250cc World Championship in 1964 on a factory Yamaha, it took a privateer team to crack open the big bike classes. In 1967, Yamaha importer Trev Deeley modified two 250cc Yamaha Twins taking them out to 350cc, and entered riders Yvon DuHamel and Mike (now Michelle) Duff in AMA road racing. DuHamel led the Indy National briefly that year before crossing the line behind H-D 750-mounted Cal Rayborn, while Duff qualified second fastest at the 1968 Daytona 200, which Rayborn also won. The giant-killing era of the nimble 350 smokers was underway.
And it was in 1967 that Yamaha launched its first 350cc street bike, the YR1. As little more than a big-bore version of the 250cc, the YR1 can trace its ancestry to the YD1 of 1957, which Yamaha engineers designed after “researching” the Adler M250 street bike and the racing RS250 Twins. These were of the then-revolutionary loop-scavenging design developed by DKW’s Hermann Weber. By 1962 the 250 had evolved into the 19-hp YD3 roadster with a pressed-steel backbone frame and electric start, joined the next year by the sporty but kickstart-only 25-hp YDS2.
The big development came in 1964 with the YDS3. Until then, almost all two-strokes were lubricated by mixing oil with the fuel, a tedious and haphazard process which often meant carrying around a bottle of two-stroke oil. Yamaha’s innovation was to carry engine oil in a separate tank and inject it into the engine at the carburetor, using use a small oil pump driven by the transmission input shaft. The fuel/oil ratio was determined by engine speed and throttle opening.

RD350B.1
In 1965, Yamaha introduced its first bigger banger, the 305cc YM1, which lasted two seasons before being replaced by the full 350cc YR1. Next to arrive, in 1970 was the five-speed R5.
The 1972 RD250 and 350s used reed valves, which allowed the port timing to be revised for more thrust and a wider powerband without mixture being blown back through the intake. An extra cog went into the transmission, while up front a disc brake provided the extra stopping power this now potent package needed. For the 1975 model year when Ian Ian’s RD350B left the Hamamatsu factory, nothing much had changed from the ’73 bike but the paint schemes.
The RD350 was universally lauded by the motorcycle magazines of the day. “Take the RD350 out on a favourite stretch of hilly, winding road where the six-speed transmission and powerful front disc brake can be used to their fullest, and you’ll find a race-bred motorcycle in a street machine’s clothing,” said one.
Ian, a former Royal Navy engineer now living in Victoria, BC, remembers a motorcycle store close to where he grew up in England.

RD350.2
“I’ve got this vivid recollection of seeing this showroom full of bikes with the 350 Yamaha in the middle and not being able to get at it,” he says. “So when I came across this one…”
Ian’s RD350 was discovered in a wrecker’s yard in Victoria and received a complete last-nut-and-bolt rebuild, with NOS replacement parts where necessary (mostly the perishable runner parts), and fasteners and chrome parts replated. The engine received a rebore with new Wiseco pistons. The frame was powder coated at Victoria Powder Coaters, while plating and polishing was done by Victoria Plating. The fork stanchions were sent back to the UK for hard chroming. Ian has found hard chroming—like that used for hydraulic cylinders—to be very expensive in North America, so he takes advantage of visiting in-laws to have parts shipped to the UK.
How about buying replacements?
“I like to use the original parts if I can,” he says. “There are more niche industries in the UK that do things like machining.”
Stainless spokes for the wheels came from Buchanans, and the wheels were trued by Ian’s local bicycle shop. “I respoked them, but I’m not very good at truing,” he says. Period Avon Roadrunner tires were an eBay find, while many obscure parts come from Action Motorcycles in Victoria, after Ian identified the part numbers from microfiche diagrams on the internet.
“I just give the guys at Action Motorcycles the parts list and they order them, even obscure rubber pieces,” he says. “Even if they come from Japan, they only take about two weeks to get here.”
Ian recovered the seat himself using a repro seat cover, while the decals came from Sunrise Graphics in the UK. For the UK-spec silver finish, he worked with Perfections Custom Paint in Victoria.
“Getting the right shade of silver was difficult,” he says, “because the only guides I had to work with were period photographs.”
Ian credits two other companies with helping him find NOS parts. “Like the top of the airbox, some of the rubber bands that keep things in place,” he says. Many of these came from Speed & Sports Inc. in Bloomberg, Illinois, and from Northwest Vintage Cycle Parts.
Reviewing the RD350B in 1975, motorcycle magazines universally praised the broad powerband, powerful brakes and stable handling. In the context of the small two-stroke bikes of the day, I’m sure their praise was warranted. But compared to modern sport motorcycles, the RD350 feels strange indeed. The rider very much sits on the bike rather than in it, perched on the narrow seat. The controls feel oddly vague and remote, while the powerband is quite narrow with limited grunt below 5,000 rpm and all done at 7,500. Handling on the period tires feels skittish and braking is competent but certainly not noteworthy.
Where the RD350 scores, though, is the fun factor. The vibrant paint, sparkling chrome, ring-a-ding exhaust note and trails of blue smoke certainly stand out in an age of cookie-cutter, plastic-wrapped four-strokes.

– Robert Smith (issue #270)