Yamaha’s Grand Prix YZ250FM.

At the start of the 2011 Grand Prix motocross season Team Yamaha unveiled a prototype fuel-injected YZ250F for Gautier Paulin to race. This is not a production bike, and although it is based on prototype bikes being tested by the Yamaha R&D department. According to sources at Yamaha of Europe, the new fuel-injected engine has a new cylinder head, new camshaft, new crankshaft, new piston, new rod, new exhaust and new intake valves. There are also rumored to be new gear ratios in the five-speed transmission.

Fuel-injected YZ250F engine.                                 Keihin-carbed YZ250F engine.

Given that the existing YZ250 has the oldest engine currently in production, an all-new YZ250F engine is long overdue. Yamaha has been working on a fuel-injected YZ250F engine since 2009…and the current aluminum perimeter frame (called “bilateral beam” by Yamaha) was designed to be used with the then-developed EFI engine. To run fuel injection, Yamaha needed a fuel pump and their old plug-and-play aluminum frame did not have room for a pump in the tank?thus, the 2010 perimeter frame was designed to allow for a flat bottomed gas tank. Unfortunately, at the time that the new frame was introduced, Yamaha was unhappy with the performance of their fuel-injected 250cc engine and made the choice to put the old Keihin-carbed version in the perimeter frame instead.

The frame is ready and the new engine will just drop in.

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