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… Read more