2006 Yamaha YZ450F
The 2006 YZ four-strokes were unveiled yesterday at Yamaha’s annual Las Vegas dealer conference, and both the YZ250F and YZ450F have aluminum frames similar to those featured on the 2005 two-strokes.
In addition to the aluminum frame, the YZ450F receives a host of changes for 2006. Chief among these are a new close-ratio five-speed transmission (last year’s YZ450F had a four-speed transmission), all-new 48mm Kayaba inverted forks, and a redesigned rear shock featuring a titanium spring for lighter weight. The engine has also received some changes – the carburetor and exhaust were redesigned for more power, the cylinder head angle was changed and the oil tank was moved inside the crankcase to achieve better weight balance. In addition, the piston, rod, and crank were redesigned for “increased performance and durability”. Finally, the piston is now cooled from beneath by an oil sprayer located in the bottom end.
The aluminum-framed YZ250F received some changes of its own, albeit not quite as extensive as those of its bigger brother. In addition to a new aluminum frame, the 250 four-stroke now features the same 48mm Kayaba inverted forks used on the new YZ450F, and the rear shock was similarly redesigned and equipped with a lightweight titanium spring. The carburetor and exhaust were again revised to increase power, and the oil tank was moved to a more forward location (ahead of the engine) to improve weight balance. Lastly, a new CDI magneto provides improved spark for the ignition system.
Both the YZ450F and YZ250F now feature ProTaper aluminum handlebars in adjustable clamps.
Yamaha claims a dry weight of 220lbs for the 2006 YZ450F and 206lbs for the 2006 YZ250F.
You might think that Yamaha would be content to leave their two-strokes alone for 2006, but you’d be wrong. The YZ125 and YZ250 also get the new 48mm Kayaba inverted forks and the revised rear shocks with titanium springs. Both bikes also get increased fork pitch (distance between the fork tubes), which Yamaha claims gives improved handling. Another change both two-strokes have in common is revised carburetion and new exhaust pipes, which are claimed to meet FIM sound requirements and still give increased power. Oddly enough, the two-strokes don’t receive the same ProTaper bars as the four-strokes, instead using Renthal aluminum bars in adjustable clamps.
One last thing: to celebrate their 50th Anniversary, Yamaha will produce a “Special Edition” version of both the YZ450F and YZ250F in 2006. These bikes will feature the classic Yamaha yellow and black graphics scheme rather than the modern blue and white.
2006 Yamaha YZ250F Special Edition