A new YZ250F is the highlight of Yamaha’s recently revealed 2019 off-road range, featuring a completely revised engine and frame.
The unusual rear-slanted cylinder idea used in the previous generation remains, but the cylinder itself is more upright and topped with a new head using a lighter throttle body and housing re-profiled cams and ports.
Inside, the piston is also new, increasing compression, and the whole thing drives through a transmission using stronger material for the gears, allowing them to be slimmer and lighter.
A larger-diameter clutch with thicker plates connects the two, and there are new radiators and exhausts to improve weight distribution.
A smartphone Power Tuner app connects to the ECU wirelessly and lets you swap and modify engine maps, including air/fuel ratios and ignition timing, and also to download datalogging information. There’s a two-position bar switch to change maps on the fly.
All this tech sits in a new aluminium frame designed to increase rigidity and give better feedback in corners. Of course, the skin is new as well, with a more compact shape and a lower seat than before, and both the forks and rear shock are improved over last year’s versions.
By Ben Purvis