also chose a fully adjustable Elka Stage
5 shock for the rear. Nonadjustable,
rebuildable Elka shocks are available for around $600. We went with
a Dominator II rear axle for its extra
strength and to match the front end’s
increased width, and we added a GPR
Low Boy steering stabilizer to minimize
jolts sent to the steering stem in rough
ADDING ENGINE AGGRESSION
Right from the dealer, the Raptor 250
engine is great for trail riders and even
beginners, but as a rider’s skill increases, so will his or her hunger for more
power. Fortunately, the Yamaha’s motor
is mildly tuned with lots of room for
more performance. Duncan Racing has
a whole catalog of mods to make the
Raptor faster, but for this project, we
settled on one of DRI’s more affordable
engine packages that provides a significant power boost without the hard-hit-ting power delivery or extra maintenance
requirements of a full-race engine.
Duncan Racing’s National engine kit
keeps the displacement at 250cc, so no
National kit for the 250
keeps the bore stock,
eliminating the need for
expensive machine work.
BRINGING THE SUSPENSION UP TO SPEED
Yamaha set up the Raptor 250 with
the best stock suspension you’ll find
on a 250-class trail quad, but fast riders can overwork the basic, non-gas
shocks, even with the stock motor.
As the non-rebuildable shocks wear,
they lose damping and compromise
the machine’s handling. Unfortunately,
Yamaha discontinued the Raptor 250R
that came with adjustable, rebuildable,
piggyback-reservoir gas shocks.
Duncan Racing has earned national
championships because they know that
handling is just as important as speed.
They strongly suggest making the suspension work well before building a fast
motor. DRI offers race-level components
for the Raptor 250 that can be tuned for
any purpose and any skill level. High-quality, rebuildable, tunable shocks are
a great starting point for getting high-performance handling from machines
with basic, non-rebuildable shocks.
For our project bike, we chose DRI’s
Lobo II front suspension kit, which
includes Roll Design A-arms and
rebuildable, adjustable Elka shocks. We
cylinder boring or crankshaft modifica-
tions are necessary. A high-compres-
sion piston, larger intake valve, high-
performance cam and head porting are
the heart of the power package. Three
compression levels—10:1, 12:1 and
13.5:1—are available with the kit. We
went with 12:1 to get plenty of punch
from the standard-bore motor. This
compression level requires 110-octane
race gas, but not the more expensive,
super-high-octane stuff. Pump gas is
fine for the 10:1 compression piston.
The $1499 kit also includes the Fat
Boy 4 stainless full-exhaust system.
DRI’s jet kit and the freer-flowing Pro
Design Pro Flow kit for the stock carbu-
retor to ensure the modified engine gets
the fuel and air it needs for maximum
The beauty of the National engine kit
is that you can build on it if you want
even more performance. DRI has big-bore options, more radical cams and
higher-compression pistons for riders
who want the fastest Raptor 250 possible.
The Raptor 250 has loads of potential. Duncan Racing’s
modifications bring big-quad performance to this small sport
The Roll Design Lobo II front suspension kit adds race-quality
shocks and wider A-arms to the Raptor, dramatically increasing
stability and bottoming resistance.