2008 Am-Pro Yamaha WR250F 1st Ride

JC Hilderbrand | July 25, 2008
We didn t hesitate to jump on Thad DuVall s Am-Pro Yamaha WR250F. The GNCC rider took the bike to victory only minutes before this photo.
We didn’t hesitate to jump on Thad DuVall’s Am-Pro Yamaha WR250F. The GNCC rider took the bike to victory only minutes before this photo.

After riding and crashing myself to near exhaustion in the morning Triton GNCC race, I had several hours to determine whether or not I would be able to ride again later in the afternoon. The thought of making another loop on the course, after the pros had finished hammering it, was not a pleasant one, admittedly. The one thing that roped me in and demanded I stop whimpering like a schoolgirl was the fact that I would be doing it on perhaps the baddest WR250F on the planet. Yamaha had arranged a test ride on Thad DuVall’s factory ride.

Watching DuVall take the checkers as the first XC2 rider was even more motivation to fasten boot buckles and cinch the helmet strap. Considering how successful DuVall has been this season, with six wins in the first nine rounds, it’s safe to say that he’s on good terms with the motorcycle. As the series heads into its summer break, TD has sacrificed one victory to his Yamaha teammate, Dustin Gibson, who trails the No.12 bike by 32 points. The bike’s smooth delivery suits DuVall’s riding style. Though he races the 250F, TD spends a lot of his time training on a 450F, but his devotion to the WR line is solid.

Up until recently, many teams have simply used the YZ-F model and adapted it to the off-road scene, but as the WR lineup continues to improve in all areas of performance, teams like the Am-Pro Yamaha squad are opting to start with the enduro machine as their racing platform. Turning a WR250F into a race bike necessitates a few changes, many of which target the bike’s extra weight. Lighting, computer, electric start and off-road specific emission controls all add significant amounts of poundage.

In an interview with GNCCracing.com earlier this year, he said, “Dude, the bike is amazing. A lot of people are like, ‘Why do you ride a WR?’ But for me, just the way I ride, especially a 450, I like to ride in a high gear. Doing that on the WR makes me smoother. On a YZ I’m like in third gear pinned, and on a WR I’m in fifth, smooth.”

WR models are proving their worth in racing.
WR models are proving their worth in racing. DuVall says the power delivery suits his personal style and makes him feel less on the ragged edge.

It’s a battle between GYT-R and Zip-Ty Racing to see who can bolt on the most parts, but the nod goes to the latter. Wheel spacers, chain adjuster, quick-change axle inserts, magnetic oil drain plug, filter cover and carb float bowl, rear brake shark fin, quick-change brake pins, waterless coolant and radiator braces all come with Zip-Ty logos on them.

We snuck in and grabbed the WR as soon as it was wheeled off the Florida podium and pointed it back out on the track. It was immediately noticeable that the race bike carried the same power characteristics, but with faster revs and more ponies available. The cylinder and head are stock but ’08 YZ250F cams and a high-compression Wiseco piston update the top end. A Ready Racing air filter feeds the all-important O2, and more of it flows via airbox mods that remove the battery holder and top portion. The battery is tossed for an E-Batt dry cell that is stored in the GYT-R skidplate.

Dropping the battery down low is one of several mods that make DuVall’s bike handle better than a stock machine. The Zip-Ty top and bottom triple clamps with 13mm offset also give the bike a nimble feel. It definitely worked quickly in the sand but without the tendency to oversteer. Much of why this bike handled so precisely compared to the stock WR250F I raced previously is the suspension.

The Am-Pro squad uses Factory Connection-tuned Kayabas that supported the larger IMS fuel tank and rider weight easily through deep whoops. Where I work the sticks with weight, DuVall works them with speed, so even though he’s only 150 pounds, his stiffer suspension setup still worked better than stock suspension for my heavier frame. Though we didn’t get to ride the entire hellish course, the roots and rollers we found did little to separate the rear tire from the ground. Traction is at a premium and always felt readily available. Bridgestone tires and foam inserts worked fine on the Florida course.

Where I work the sticks with weight  DuVall works them with speed  so his stiffer suspension setup still worked better than stock suspension for my heavier frame.
A set of YZ250F cams, FMF 4.1 exhaust, carb settings and airbox mods wake the motor up enough to make lifting the front end in sand much easier than on a stock bike.

We were pleased at how the WR-F takes less energy to ride than a YZ-F, but DuVall’s machine is even more impressive. The extra power from the engine mods and FMF 4.1 exhaust system give it enough oomph to lift the front wheel when needed. The stocker often falls a little flat or can’t rev quickly enough to get the bike up on top of the sand which results in hitting a lot more obstacles and subsequently more wear and tear on a rider. DuVall uses a GPR steering stabilizer to minimize the effects of any front-wheel impacts.

Speaking of excessive abuse, the clutch is one area that gets worked over in the sand. Our stock bike actually held up fine, but Am-Pro sources the GYT-R catalog and aftermarket companies for these parts. The clutch basket, pressure plate, hub and cover are all Yamaha racing upgrades, and the stock cabled unit has been swapped out for a Magura Jack hydraulic system which is tucked away behind triple clamp-mounted Cycra pro bend handguards. It felt light and responsive, even after three hours of TD doing his worst.

A Boyesen water pump impeller and cover assist in keeping the quarter-liter engine cool. Stock radiators are used with Zip-Ty waterless coolant, braces and a 1.6 cap to prevent boiling, but the coolant overflow bottle has been removed for weight. And since it’s a closed-course machine, all the emission restrictions have been tossed as well.

Even though DuVall is only 5 6  it was comfortable for our tester to ride his machine while sitting or pounding through whoops.
Even though DuVall is only 5’6″ it was comfortable for our tester to ride his machine while sitting or pounding through whoops.

There isn’t much that’s been overlooked on this racebike, but compared to many of the other top pro machines, especially ones that begin life as a motocrosser, it can seem almost simple. A huge key to off-road success lies in consistency and reliability. DuVall and his Am-Pro team have spent plenty of time working off the strengths of the stock WR250F and bolstering its race credentials. Even though the odometer and kill switch have been removed, the electric starter still works just fine. This is a bike that anyone could build, at least anyone who likes their headlight to shine brightly.

Am-Pro Yamaha WR250F Spec Sheet
Triton GNCC, Florida

Rider: Thad DuVall
Exhaust: FMF 4.1 system w/Megabomb head pipe
Radiators: Stock w/Zip-Ty waterless coolant, Zip-Ty Braces and 1.6 radiator cap
Water pump: Boyesen cover and impeller
Handlebars: Pro-Taper EVO, CR-Mid bend
Grips: Pro-Taper w/Pro-Taper blister busters
Hand Protection: Cycra pro bend w/enduro shields bolted to Zip-Ty triple clamp mounts
Carb Mods: Merger racing adjustable leak jet circuit and fuel screw, Zip-Ty Racing magnetic float bowl, cut throttle stop.
Jetting Specs:
Needle-NFER, Clip 4th from top

Even without his goggles  DuVall used the super-smooth Yamaha to win in Florida.
Even without his goggles, DuVall used the super-smooth Yamaha to win in Florida.

Pilot Jet- 42
Fuel Screw- 2 turns out
Leak jet screw- 3/4 out
Oil Filter: Ready Racing filter w/Zip-Ty Racing magnetic cover
Ignition: Stock w/custom modified wiring harness
Clutch: GYT-R Basket, pressure plate, hub, clutch cover w/ Magura Jack hydraulic clutch
Brakes: Stock w/EBC pads and fluid, rear brake pedal has brake snake installed, Zip-Ty Quick change brake pins
Engine Lubricant: Yamalube
Cables: Motion Pro T2
Cams: 2008 YZ-F
Head: Stock
Transmission: Stock
Cylinder: Stock
Rear Wheel: Stock w/EBC rotor and Zip-Ty wheel spacers
Front Wheel: Stock w/EBC rotor and odometer replacement spacer
Airbox: Cut battery holder and top out
Air Filter: Ready Racing
Battery: E-Batt dry cell rechargeable battery that is located in the skid plate
Skid Plate: GYT-R
Gearing: Stock w/MSR sprockets
Chain: Tsubaki w/rivet master link
Chain adjusters: Zip-Ty Racing
Piston: Wiseco High compression
Triple Clamps: Zip-Ty upper and lower w/13mm offset

Thad DuVall has put his Am-Pro Yamaha on the podium six times before the summer break.
DuVall (center) has put his Am-Pro Yamaha on the podium six times before the summer break.

Stabilizer: GPR w/bolt on post
Suspension: Stock w/Factory Connection valving
Disc Protection: Zip-Ty Racing shark fin
Oil Drain Plugs: Zip-Ty Racing magnetic
Footpegs: Fastway w/spike cleats and KFMS bolt welded
Tires: Bridgestone front and rear (18″) w/Bridgestone mousses
Plastic: Cycra w/powerflow shrouds
Fuel Tank: IMS oversized w/dry break and Zip-Ty petcock knob
Axels: Stock w/Zip-Ty quick change inserts
Lights: Stock
Chain Guide: TM Designworks guide and buffer
Other mods: Kill switch, odometer, coolant overflow bottle, emission piping and hoses removed and emission holes plugged. Zip-Ty Neutral safety switch plug installed.

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JC Hilderbrand

Off-Road Editor| Articles | Hilde is holding down the fort at MotoUSA’s Southern Oregon HQ. With world-class dirt bike and ATV trails just minutes away, the hardest part is getting him to focus on the keyboard. Two wheels or four, it doesn’t matter to our Off-Road Editor so long as it goes like hell in the dirt.

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