1972-yamaha-yds7_1

Yamaha has a great history of air-cooled 250 and 350 parallel twins going back to the 1950’s. Their “prototypes” were German two-strokes. A 1957 production license for the German Adler twin, the typewriter company, gave Yamaha an engineering launch point for their own original YD 250 twins. Amazingly by 1958, five high pipe racing versions the YDS1, the YD-1, were sent with Fumio Ito and other Japanese riders to race the Catalina Grand Prix off the coast of California. Ito brought his high-revving twin home in sixth place.

This YDS7 model is the last of the non-reed valve piston-port induction machines, just before the RD250 and RD350 with reed valves came on the scene. In this era the street bikes took engineering design from the best of the Yamaha production road racers of the time. The racers were sold pretty cheaply and with a bit of tuning/timing setting were ready for the track. Likewise, street bikes like the YDS7 and RD’s could be stripped to the essentials, have low bars and race tires installed and be ready to production road race. On a tight road course, or in a drag race, they were giant killers to be sure.

The 250cc twin two-stroke made 30 horsepower at 7,500 rpm. Top speed if you really tucked in was 93 mph. Magazine testers reported a 1/4 mile in 14.8 seconds. The 12 volt battery ignitions were good, but flakey ignition timing or seal leaks could cause a piston seizure. The primary is helical gears, the transmission is a constant mesh five-speed. These bikes were all “oil injected” meaning there was no need to premix the gas and oil.

Specifications:

    • Engine: Parallel Twin, Air-cooled
    • Type: Piston Port
    • Bore & Stroke: 54mm x 54mm
    • Displacement: 247cc’s
    • Carburetors: Two 26mm Mikunis
    • Ignition: Points & Coil
    • Lubrication: Pressure Fed
    • Horsepower: 30HP@7500RPM
    • Primary: Gear Driven
    • Clutch: Wet, Multi-Plate
    • Transmission: 5-Speed
    • Final Drive: Chain
    • Frame: Double Cradle Steel Tubing
    • Suspension: Telescopic Fork / Twin Shocks, Swingarm
    • Brakes: 180mm Dbl. Leading Shoe / 180mm Single Leading Shoe
    • Wheels: 3.00 x 18 / 3.25 x 18
    • Wheelbase: 51 Inches
    • Weight: 315 Pounds
    • Top Speed: 93MPH
12 replies
    • john burns
      john burns says:

      I had one of these But was hampered by as said above ignition timing causing partial piston seizure. Changing the right hand spark plug cured it, but every 200 miles?? Went back to the Factory 2 or 3 times. at Chessington, they couldn’t put it right. only found out a few years later that 71/72 DS7 had this common problem. Sold it after a year. It really did motor for a 250. Lovely light bike to flick around, and the sound Heavenly…..And I love the smell of a two stroke.

      Reply
  1. ray
    ray says:

    The Yamaha 350s were hard to beat – even with larger displacement bikes. So ….. I bought a Kawasaki H2 750 triple 2-stroke and got the job done.

    Reply
      • Ron Ecke
        Ron Ecke says:

        As of 6/26/21 listed for past week in the local Craig’s List is a Yamaha model DS7, 250cc.
        Check ERIE, PA CRAIGS LIST,
        Looks good in pics, but I would see it in person of course.
        Seller is in Conneaut, Oh, about 1/2 hr drive from Erie, Pa
        I only hope you read this soon !
        Ron

        Reply
  2. Tim Olson
    Tim Olson says:

    I bought an RD 250 in the fall of 1972 and have a picture my Mom took of me on it in our yard. It was a “warm” November day by Minnesota standards.

    Reply
  3. Gary Higby
    Gary Higby says:

    When I was young my first vehicle I purchased was a Yamaha R5 B.
    It was incredibly quick to the point it scared me. The front end would pull a wheelie in the first 3 gears.
    I had it going an indicated 105 mph within 10 minuets of owning it.
    Great bike. I wish I had it today, unfortunately I had an accident with it and it was done.

    Reply
  4. john burns
    john burns says:

    I had one of these But was hampered by as said above ignition timing causing partial piston seizure. Changing the right hand spark plug cured it, but every 200 miles?? Went back to the Factory 2 or 3 times. at Chessington, they couldn’t put it right. only found out a few years later that 71/72 DS7 had this common problem. Sold it after a year. It really did motor for a 250. Lovely light bike to flick around, and the sound Heavenly…..And I love the smell of a two stroke.

    Reply
  5. Philip Drewell
    Philip Drewell says:

    I had one of these from new in ’71 but got rid of it when it tried to kill me in a tank slapper on an elevated road. Not only did I have to change my trousers, I changed the bike for something that handled better, a BSA Lightning.

    Reply

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