TAMING
yo u pro bably already know,
the big new s comi ng o ut of
Yamaha has be en the all-new
aluminum frame on their 2005
25 and 25 0cc tw o -st ro ke s.
Even though the Yamaha four-strokes did not
A
rece ive the same treatmen t, t hat doesn't
mean that the yz Fs, in thiscase the YZ450F,
didn't get its fair share of atte ntion, too. No,
the Fs didn't just get BNGs for 2005. Instead,
Yamaha decided that the powerful YZ450F
thumper needed a little mellowing o ut and
spent a lo t of time maki ng t he mighty
yz450F easier and more forgiving to ride.
The 2004 YZ450F was anything but
mellow and for many was quite t he handful. 50, w ith this in mind, Yamaha sat down
and t hought of a few creative ways to tame
the beast. After months of te sting, te sting
and more test ing, Yamaha is confide nt t hat
they came up with the ideal big-bore fourstroke mo tocrosser.
First , Yamaha started out by redesign ing
t he airbox, and then they moved on to the
28 SEPTEMBER 22, 2004 • CYCLE NEWS
40th Anniversary
e ngine . The airboot has been reshaped and
is shorter, whic h Yamaha claims improves
air-intake efficiency and thu s smoot hes out
the power.
lntemally the cylinder head has also bee n
,
tweake d and the com pression ratio reduced.
The intake port has also been reshaped to you guessed it - smooth out the power.
Moving on , Yamaha also tinkered with
the carburetor. They changed the setti ngs,
moved the needle screen up two millimeters and lowered the main nozzle jet.
All of this com bined helped to improve t he
fuel mixture at low RPM and - once again to help smoot h out t he power delivery.
Altho ugh these changes to the moto r
seem minor, you can certainly feel the end
res ults on t he track. The yz is still a rocket ship and pumps out tons of power, but
the hit isn't qu ite as ex plosive as last year 's.
That's certain lygood news for us "no rma l"
humans, but we expect t hat so me of the
faster experts and pros might feel oth er wise . But this bike sho uld appeal to a
