Yamaha built a successful line of YDS 250 cc two-stroke twins in the 1960s, which eventually grew into the 350 cc YR series. The 1970 YR5 produced 36 bhp and had a top speed of 95 mph. This grew to 100 mph in the RD 400 of 1976, and the water-cooled, single-rear shock RD350LC of 1983 gained a YPSV exhaust power valve, bumping horsepower to 53.

The RD350LC dominated the 350cc Grand Prix class until it was discontinued in 1982, and Yamaha brought the technology to the street in 1983. The result was a 350 cc water-cooled, 330 lb twin with a six-speed featherbed frame, aluminum rear swing-arm, single rear shock and disc brakes.

The 350LC (known as an Elsie) could do the quarter mile in 13 seconds and had a top speed of 121 mph, and the exhaust power valve varied the port timing as the revs rose and fell, which broadened the power band significantly. In both full- and half-faired versions the LC would be sold all over the world, and as late as 1996 in Brazil.

The two-stroke RD 400 disappeared from U.S. markets in 1979 when it became the victim of emissions regulations, so it was surprising that Yamaha introduced the RZ 350 in 1984. Yamaha overcame emissions regulations through stringent controls, including a catalytic converter. It was the first motorcycle to employ one.

Two 1984 models were offered – the yellow and black Kenny Roberts signature edition and a red, white and blue model with different graphics and no Kenny Roberts name on the upper cowl. In 1985, red, white and blue versions had identical graphics to the yellow and black "bumble bee" Kenny Roberts version, complete with signature, and a red frame. Some leftover models with revised graphics resembled the 1983 European versions with gold wheels and a Kenny Roberts signature. These were sold as in California in late 1985-86.

The Kenny Roberts Edition has cachet in the U.S., as Roberts was the first American to win a World Road Racing Championship in 1978. He had previously won two U.S. Grand National Championships in 1973 and 1974 including winning the Grand Slam of all four categories.

Roberts’ main legacy came from his revolutionary riding styling. He was the first successful racer to hang completely off the bike and touch his knee down. The Kenny Roberts RZ 350 makes his case perfectly, as an experienced RZ rider can keep up with much bigger machines on twisty roads using that aggressive riding style.

U.S. RZ 350 production was about 20,000 motorcycles, and a good number have survived in collections. This is partly because they are among the last two-strokes sold in this country and partly because they are quick and great fun to ride.