Yamaha was the first manufacturer to
switch from full worksbikes to
modified production machinery, and
the 1990 Yl250 gets an in-house
modified cylinder witheither a Pro
Circuit or Bill Pipe's exhaust,
depending on rider preference. The
modified silencers are shorter than
stock but still meet noise
requirements. Both front and rear .
Kayaba suspension units are detailed
byYamaha. Magnesium is used for the
triple clamps, hubs and rear brake
carrier, and titanium is also used for
various parts. Askid plate is added to
the frame, and Alumilite bars replace
the stock units.
Pro Cil'Cllit ha...les tile motor
lIIodifications 011 Keith Johnson's KTM
250. The carburetor is rejetted and
KIM is experimenting with a 37mm
DeIl'Orto carburetor to replace the
stock Keihin carbo Both front and rear
suspension components are revalved
with heaviersprings, and the front
forks are pre-production 1991
models. The standard shift lever is
replaced with a stronger unit from a
KYM 600cc four-stroke. Johnson
prefers a taller seat from Ceet Racing
and Renthal handlebars.
Jeff Emig's KX125 is basically a stock unit with extensive porting allll CYlinder
head modifications. Aluminum triple damps bold 1989 Kayaba factory forks with
updated parts, and the productiOll rear shock is revalved. Jeff Matiasevich will get
the mapesium and titanium parts used on the 250, plusfactory motor, for his
12See National bike.
8lMIdy AmlHZ's RM12SL gets tile same _ificati. . as tile RM25O.
.
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