Yamaha DT 250

Something of a two-stroke riposte to Honda's SL350, the RT-1B was a logical successor also to Yamaha's own 125 and 250 on-off road bikes of 1969/70.

Rather tall, but decidedly handsome, it had an iron-barrel, alloy-head engine nominally of 360cc, actually of 351 cc, with over-square (80 x 70mm) measurements, employing Yamaha's newly evolved five-port configuration. In this system the then-conventional three ports were augmented by extra passages to the rear of the transfer ports, designed to direct the incoming charge as a boost toward clearing the cylinder of spent gases from the preceding power stroke. Power of the RT-1B was programmed from 2,500 rpm through to 6,500, at the tachometer red line. Lubrication was by Yamaha's usual Autolube, with a special high-capacity pump to give more oil for the large single. An unusual feature was the additional tapped hole in the cylinder head, to take a compression-release fitting, should the owner wish, or a spare sparking plug.

Contributing to the high riding position was the 10in ground clearance beneath the crankcase 'bash' plate; handling, though, was rated as fair to good, mainly because of the appealingly low weight of 270 lb.

The compromise nature of the bike,
very typical of earlier Japanese efforts in the trail/enduro bike field, was shown by the (not very) quickly detachable lighting set, and direction indicators mounted in the middle of the high, braced handlebar and on vulnerable 'ears' behind the short dualseat. However, the RT-1 B was rather more than an off-duty plaything, for an example was first motor cycle finisher in the arduous Baja 1000 of 1971.