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By Cliff Montgomery,
Over the last few years, 250cc four-stroke motocross bikes competing in the 125cc class have swelled from a single Yamaha YZ250F to four potent, easy-starting, fairly light track weapons that are all but unbeatable on starts. The big question is: Which ones are some of the very best?

Kawasaki KX250F/Suzuki RM-Z250

A few years ago Kawasaki bought out Suzuki, or at the very least its motorcycle division. In a money-saving effort the people at Kawasaki have used the same engine for both the 2005 Kawasaki KX-F and the Suzuki RM-Z250.

The motor on the Kawasaki/Suzuki twins is quite an eye-opener. On the track, the motor revs the furthest and builds revs the fastest, but it almost feels as though it has two powerbands: one that pulls from the bottom up through the upper midrange, and a second rush during the overrev. That is, the engine gets a little lazy up top, then kicks in again for the overrev portion of the power.

Many feel the 2005 motor is a great powerplant for clearing short run-up jumps. Most of the time, and during most track conditions, the KX-F/RM-Z's power is snappy and usable, and the stock Kawasaki jetting work quite well on the track.

Some have experienced a few shifting problems with dirty oil in the KX-F/RM-Z; once the oil is changed it shifts fine. But on the plus-side, riders have no problems re-lighting the motor after any tip-overs.

The KX250F/RM-Z250 is close to being perfect...if it just had better suspension.

+Strong motor characteristics
+Great handling
+Very light feeling
+Starts much easier than last year's bikes
+New radiators help the bikes to run coolly
-Kayaba suspension is outdated
-Steel handlebar is cheap; needs aluminum handlebar as other bikes in its class

Yamaha YZ250F

Off the bottom, the YZ250F motor is a bit soft and will hiccup or hesitate if you try to roll the power on quickly with the throttle. It requires a bit of clutch to get going, but once the revs pick up it generates a very strong midrange and top-end, with a nice dose of overrev. With some clutch the Yamaha makes it easy to get the power to the ground and tackle any obstacle in its way. The transmission shifts smoothly under power, and the clutch has a nice, light pull to it with zero fading.

The Yamaha pulls especially harder than the other bikes on top. The power just never seems to go flat. Of all four bikes in our study, the YZ-F has both the brute muscle and the best reputation for mechanical longevity.

Yamaha has understandably been criticized for the weight and complexity of its dry sump engine, which carries the oil in the frame. That design complicates removing the engine from the frame, but having the oil in the frame lets the frame itself act as a giant oil cooler. That in turn accounts for some of the Yamaha's reliability, so it's a give-and-take.

+New Kayaba suspension works immensely better than last year's model
+New gripper seat cover truly works
+Comes stock with Renthal aluminum handlebar
+Strong motor characteristics
-Plastic still looks fatigued after minimal use
-New Renthal handlebar has odd bend
-Center of gravity feels high

Honda CRF250R

For 2005, Honda engineers made a few minor changes to the motor, and those mods help it bolt out of tight turns faster and harder. The 2005 model shines during uphill pulls and right-out-of-turn jumps. The CRF250R is deceptively smooth and constant at very low rpm. The midrange is where the power comes on strong and pulls hard into a really quick top-end with a bit of overrev. The CRF doesn't produce a hard-hitting sensation as does the YZ-F or the KX-F/RM-Z, and is also a little shy on total boost. The difference is more distinct when the track surface is soft, sandy or muddy than it is on packed terrain.

Compared with the other three bikes, the motor on the CRF has clean roll-on power at a lower rpm. The power gets to the ground in a controllable fashion, and you can tell what the bike is doing at all times. The clean shifting is a help, since the Honda demands slightly more gearbox action than the other bikes.

The CRF's Showa suspension is what puts the Honda ahead of the competition. Although the Yamaha's new Kayaba suspension is close, the Showa fork on the CRF is damn near perfect, period.

+Feels light and responsive to rider input
+Easy to start, hot or cold
+Very comfortable riding position and great ergonomics
+Retains new look for a long time
+Comes stock with Renthal aluminum handlebar
+Brakes have excellent stopping power
-A bit cramped for really tall guys
-Piston and valve replacement intervals are shorter than for other four-stroke models
-Clutch is vulnerable to abuse

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