Back in the olden days, Yamaha had a reputation for making powerful 125s. From the (unrestricted) air-cooled RD125DX two-stroke twin of the 1970s, through to the amazing-when-derestricted TZR125 of the 1990s, the tuning fork folks knew how to get the most from an eighth of a liter. They’ve done it again with the new R125. Amazingly, the new bike has a fully-fledged variable inlet valve system in its little four-valve cylinder head. The single overhead camshaft has two intake cam profiles – one high-speed and one low-speed.
The intake valves are operated by a two-piece rocker arm, with one follower on each cam profile. Below 7400rpm, only the low-speed cam profile follower operates the valves, giving great torque and efficiency. Over 7400rpm, an ECU-controlled solenoid moves a pin which locks the two-part rocker arm together and letting the high-speed follower take over. So the valves are opened for more lift and duration, giving great peak power. Okay, the total output is still limited to 15bhp; this is still a learner legal bike, of course. But on the road, the little Yam feels by far the best of all the 125s I’ve ridden in recent times.
The engine has a proper power curve and actually feels like a ‘real’ powerplant. On the Tarmac of our test location just outside Valencia, the R125 hit an indicated 130kph easily enough – nearly 80mph in old money. Engine apart, the rest of the R125 also gets top marks. The steel Deltabox frame, alloy swingarm, USD forks, and radial four-piston front caliper definitely make it the class leader in the learner sports bike sector… and a worthy successor to the likes of the RD125 and the TZR.