Retrospective: Yamaha RD350: 1973-1975
(This Retrospective article was published in the August 2008 issue of Rider.)
STORY AND PHOTOGRAPHY BY CLEMENT SALVADORI
Nicknames can be good, flattering, positive…or quite the opposite. In the case of Yamaha’s RD series, the Chef Boy-Ar-Dee moniker—say it slow—was greeted with less than enthusiasm by the company execs in California. After all, that RD was meant to stand for Race Developed, not a can of Americanized overcooked pasta. Grin and bear it.
The Chef Boy 350 was an updating of the venerable R5, a mainstay of the company’s line. In this day of 100-horsepower 600cc sportbikes it takes some mental acuity to go back to when a 350 was considered a two-wheeled weapon of consequence. Kawasaki had come out with its 350 triple, the Suzuki GT380 was no slouch in the performance department, and Yamaha wanted some of that market.
In the middle ‘70s the company had a split personality with its street models, seeing the EPA’s handwriting on the wall: Two-strokes would not be forever. With this understanding Yamaha’s major focus was on the four-stroke TX series—500, 650 and 750 twins, less advertising for the smaller, definitely cheaper two-stroke twins. The 1973 price for the RD350 was $839, while the TX500 came in at $1,350.
The RD350 was essentially a reworked R5 350, with identical 64mm bore and short 54mm stroke and 28mm carbs, sitting in a cradle-type tubular frame. Yamaha’s reliable Autolube oil-injection system had a tank holding more than half a gallon of oil, good for a long run. What, then, was new with this Chef Boy 350? Quite a bit. The engineers had taken the R5’s engine and put in seven ports and reed-valve induction…called Torque Induction by the ad guys. For those who have never been familiar with two-strokes, the reed valve—a success on Yamaha’s single-cylinder motocrossers—was a bit of high-tech sophistication, using a very light, very thin, very flexible piece of metal between the carburetors and the cylinders that would open when there was any vacuum within the engine caused by the exhaust gases flowing out, allowing the air/oil/gas mixture in. It closed when the pressures were equal, preventing any possibility of the fuel getting shoved back out the carburetors, or “blow-back,” as Yamaha liked to call it. Add that to multiple ports, with half-a-dozen allowing for normal intake and exhaust work. The seventh port threw in an extra hit of fresh mixture at the last micro-second that served to cool the piston dome, as when the fuel went in through the crankcase it warmed up as it flowed to the combustion chamber. All a bit confusing to the four-stroke mind, where we think of valves rather than ports.
What this did was add a little more power in an ever-narrower powerband. Horsepower and reality were at odds, with Yamaha immodestly claiming 39 mustangs at the crankshaft. However, when the unromantic editors at Cycle magazine had the temerity to put the RD350 on a dyno, they found only 30 thoroughbreds at the rear wheel. In truth, 30 horsepower out of a 350 was not bad, but these came on at 8,000 rpm, and at 6,000 rpm the number dropped to 20; keeping those 20 to 30 horses at full gallop meant doing a lot of shifting, so Yamaha added a sixth gear to the transmission.
The engine work made it a little more finicky to ride, but really more fun. You could set the tach at 5,500 in sixth gear and cruise at 70 mph, or keep the engine on the boil and howl along the back roads. The bike was weak on torque, but if the rider happened to hit the powerband in first or second gear, that front wheel would reach for the sky. The suspension was a trifle on the soft side, and various bits could drag in the corners if the rider were cheerfully aggressive, but the great advantage was the new 10.5-inch disc brake on the front wheel, with the caliper having two slave cylinders pushing the opposed pucks that ferociously squeezed the disc. Everybody loved the new brake. On the rear was a standard drum. Tires were a 3.00 x 18 on the front, 3.50 x 18 on the back, with 52 inches between the axle centers.
Over the headlight was a simple dash, speedo and tach on either side, a key in the middle, two lights indicating turn signals were on, high beam—and a light to tell the rider if the brakelight was not working. The ignition key was also good for unlocking the gas cap, unlocking the saddle, and locking the steering head. Gas on, choke on, key on, kick. No electric starter on this dandy, not that one was needed. It had good manners, and even cold was a two-kick affair. Burble off down the street, out into the countryside, and with the properly warmed engine, screw that throttle down! There was a big noise as the carbs gulped air. The RD weighed 350 pounds with full gas and oil tanks, and a competent lightweight rider could hit 90 mph from a standing start in under 15 seconds.
Hot-rodding this little gem was a growth industry from the moment the Chef Boy appeared, with a great array of bolt-on goodies. Within weeks the café boys could buy a bikini or full-race fairing, light fenders, a bigger gas tank, clip-on handlebars, rear-set footrests and any manner of high-performance expansion-chamber exhaust systems. Aftermarket wheels allowed for wider, low-profile tires. Koni could supply far better shock absorbers. For anyone wanting to get into the engine, the pocketbook was the only limit. If anybody doubted the ability of a two-stroke 350 twin to run, all they had to do was take a ride on Yamaha’s TZ350, a liquid-cooled production racer that put out more than 60 horsepower. The single most popular bike in club racing was the RD350.
The Race Developed Ar-Dee stayed on the Yamaha charts for only three years before undergoing considerable changes and becoming the RD400 (Retrospective, October 1991). Not much was altered in those three years other than the MSRP, as the ’75 model cost $1,071, a whopping great 25 percent increase in price over the ’73.