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Yamaha YDS7
In the evolving line of Yamaha two-strokes, the
YDS7 of 1971 is notable as the one in which the till-then popular rounded look
was replaced by a more angular line, at the same time becoming slimmer, lower
and lighter.
Peak power of the YDS7 was set at 7,500rpm which, with top (fifth) gear engaged,
came up very easily, the bike being a trifle undergeared, and worked out to a
road speed of 90mph.
A small rider, crouched, could extract a further
5mph with no great difficulty. Steering geometry (62.5° castor, 4.2 in trail) to
give a fast response made the bike very diverting transport on winding roads;
30bhp, combined with the effect of a short wheelbase (54in) and low weight
(300lb), would keep the front wheel in only light contact with the tarmac.
For this model Yamaha introduced an 'excited
field' generator for ignition purposes, which worked well and emitted an eerie
whistle as the ignition key was first operated and the system set itself up. In
this connection, a more obvious step forward for 1971 was the positioning of the
ignition key in the top of the steering head instead of under the nose of the
tank.
Yamaha YDS7 Specifications
Engine air-cooled, piston-port, two-stroke
parallel twin
Capacity 247cc
Bore and stroke 54mm x 54mm
Power 30bhp @7500rpm
Torque 21ftlb @ 7000rpm
Carburettor 26mm Mikuni
Ignition Mitsubishi contact breaker
Transmission Five-speed, wet clutch, chain
final drive
Frame Steel tube twin cradle
Suspension 34mm telescopic forks. Twin shock
rear
Front Brake 180mm twin leading shoe front,
180mm single leading shoe rear
Wheels 300 x 18 front, 3.25 x 18 rear
Weight 143kgs
Wheelbase 1300mm
Fuel capacity 12ltrs
Top Speed 93mph
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