By now, it's a well known fact that the YZ 400's most
striking feature is its engine.
Don't look for older model Yamaha XT and TT engine model parts on Yamaha's latest 4-stroke offering. Yamaha built the YZ 400 engine based on computer modeling studies. It shares little, if anything, with its ancestors.
Power is generated in the ceramic composite plated cylinder via 5 valves: three intake valves and two exhaust valves. Chain driven, dual overhead camshafts perform the valve lifting duties. A single port exhaust exiting into a single header pipe performs the exhaust chores Advanced technology abounds on the YZ 400. The new YZ 4-stroke engine is designed to run on 92 octane gasoline. This unusual stoichiometric accomplishment is achieved by employing a very unique carburetor and digital (computer microchip) ignition system.
This ignition system works like this: The 400's transmission ratio's are the same as the '98 YZ 250's; however, the transmission gears and shafts aren't interchangeable between the models.
Chassis wise, the '98 YZ 400 and the '98 YZ 250 share the same
chassis! The differences are the YZ 400 carries an oil tank near
the steering head, some of the engine/lubricating oil is carried in
the front part of the frame, and the YZ 400 has stiffer fork and shock
springs. Rake, trail, forks, shock, and swingarm linkages are the same
as the YZ 250.
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