CUSTOM BUILD: DUNCAN RACING HONDA 250R

Simply a showpiece By the staff of Dirt Wheels

This Duncan Racing masterpiece sits on a set of Maxxis MX comp tires mounted on OMF beadlock wheels. The rider sits on a Pro Top cover by Zip. Duncan’s signature chrome front bumper and the super-rare Lobo chassis help it stand out even more.

After only four years in production (1986–1989), the Honda Fourtrax 250R became the most popular sport ATV of its time, and they sold tens of thousands of them easily. In the 1990s and early 2000s, many were transformed into masterpieces like what you see here. It was a time without current production machines to build and compete with, but that didn’t stop hungry racers from using the best, and at that time, it was hands down the best 250R two-stroke. Today, modern four-strokes have evolved, and most production rules have been lifted so racing a new YFZ450R or even a Honda TRX450R from 2014 still makes sense for the track. However, that doesn’t mean the trick two-strokes are not still being built. In fact, Duncan Racing recently completed an absolute showpiece for a customer in Europe. Before it was boxed up and loaded on a plane, headed to its new owner, we rolled it into our studio for all to drool over.

Roll Design swaps out the stock aluminum swingarm for a much stronger steel unit with improved geometry. This one has a link setup with a long Stage 5 Elka shock and a Dominator 2 axle. The sprocket is a 38-tooth from Sunstar, and the chain is a 520 from RK.

PARTS LIST

Main contributors: Roll Design

Special thanks: OMF, Paul Turner Racing, Hinson, RK Chain, Maxima, 

Machine: 2018 Duncan Racing/Roll Design 340cc Lobo ATV

Quad weight: 350 lb.

Chassis: Roll Design Lobo MX Assy

MOTOR

Motor (type and origin): 2-stroke Honda TRX 250R base Equipped with Duncan Racing PC 2000 340cc power valve, Nikasil-plated cylinder)

Bore/stroke: 77.50/72.00

Displacement: 340cc

Porting: PC 2000 midrange

Head/head mods: PC 2000 head

Ignition/ignition timing: OEM TRX 250/billet adjustable timing BRG holder

Spark plug/spark plug gap: NGK BR9EVX .028”

Reed cage: Pyramid Reed Valve

Carburetor type and size/carb modifications: Keihin 39 w/DR Super Flow

Airbox material and brand/air filter brand/air filter oil: OEM Box, K&N filter

Pipe/silencer: Paul Turner Eliminator pipe & Fat Boy silencer

Radiator origin/material: CBR

Fuel/fuel octane: VP C12

2-stroke oil/2-stroke oil ratio: Maxima 927 32-1

Engine oil: Maxima MTL Endurance

These are Honda TRX450R spindles and brake calipers with Galfer rotors and Crown Series steel-braided lines filled with Maxima fluid. Movement is all handled by an Elka Stage 5 fully adjustable shock.

DRIVE SYSTEM

Clutch basket/plates/springs: Hinson basket/ DR C12 clutch kit

Transmission/tranny oil: Yukon HD Trans Gears, Maxima MTL 

Chain/chain lube: RK 520 O-Ring Chain/ Maxima Chain Wax

Sprocket brand f/r: Sunstar

Gearing f/r: 15t C/S front & 38t rear

FRONT END

A-arms: Roll Design Lobo

Spindles/hubs: TRX450R

Front end overall width: 50” w/ tires

Front shock brand: Elka Stage 5 *Shocks customized by Roll Design

Steering stem: Roll Design

Roll Design’s super-wide footpeg has been an aftermarket favorite for decades, and the IMS Roll nerf bars are light, simple and in this case without a heel guard, like they used to run back in the day.

REAR END

Swingarm brand and material/swingarm length: Roll Swing arm

Rear axle/rear axle width/axle carrier: Dominator axle/Millennium carrier/ 49” wide

Rear shock brand: Elka  

TIRES/WHEELS/HUBS

Tire brand f/r: Maxxis Tires

Wheel brand f/r: OMF custom beadlock

Rear hubs brand and material: OEM R. Hubs

Stock 250R hubs were powdercoated blue to match the outer beadlock rings on these OMF wheels. This inner ring not only looks cool, but it helps the lightweight wheel stay strong.

BRAKES

Brake calipers f/r: TRX 450R

Pads f/r: OEM

Rotors f/r (diameter and brand): Galfer

Brake lines: Crown Series steel braided

Brake fluid: Maxima 550

In the ’90s, a race quad like this would cost over $25,000 to build. With the lack of OEM parts today and rising costs everywhere else, the price would be doubled. 

HANDLEBARS/CONTROLS

Handlebars brand and bend: Pro Taper

Throttle type: Billet

Clutch perch: Works Connection

Cut-off switch: Pro Design

A Roll steering stem holds Pro Taper bars a billet thumb throttle and a Works Connection clutch lever. Maier Manufacturing OEM-style bodywork and tank cover sits over a stock-sized IMS gas tank. For a build like this, OEM plastic is nearly impossible to find. Maier Mfg. equipment is just as good and comes in a variety of colors. Roll Design was a pioneer in ATV chassis development. Their gull-wing A-arms and the rest of the Lobo chassis were way ahead of their time. Now paired with modern Elka shocks, the combo is nearly impossible to beat. The number of riders that ran the number-one plate for Duncan is more than a mouthful. Just to name a few, like Marty Hart, Doug Eichner, Travis Spader, Bob Sloan and Gary Denton, brings back memories.

DETAILS

Nerf bars/front bumper: Custom Roll aluminum nerfs, DR Chrome F. bumper.

Skid plates brand/skid plate location: N/A

Fuel tank material/fuel capacity: IMS tank/stock capacity

Seat cover: DR/Pro Top by Zip

Body material and brand: Maier OEM style plastic/white f. nosepiece/tank cover

Footpegs: Roll Design S/S

At the heart of this build is a massive 340cc, two-stroke with a power-valve-equipped Nikasil-plated cylinder. There is a Pyramid reed valve sandwiched between the jug and a 39mm Keihin PWK carb.

OTHER SPECIAL SETUPS, PRODUCTS AND MODS

Polished components: Complete engine

Chromed components: Steering stem, subframe, upper A-arms, Powdercoated components. Frame, swingarm, lower A-Arms, r. brake pedal

Other special mods/setups: DR quick-change clutch cover mod, DR billet shift lever, DR “race team” graphics kit, DR dual O-ring steel exhaust flange

A Paul Turner Racing expansion chamber mated to a Fat Boy silencer extracted even more ponies out of the monster. The Yukon HD trans gears and Hinson clutch are hidden behind the polished case and gets that power to the ground. Some of only a few other stock components are the kick-starter and brake pedal.

CONTACT

Duncan Racing International, Inc.

9380 Bond Ave, Suite B

El Cajon, CA 92021

Voicemail: (619) 258-6306

Fax: (619) 258-6309

www.duncanracing.com

ATVCBRDuncan RElkaFatBoyHinsonHonda TRX250RLoboMaxxisOMFRace QuadRoll DesignShowpiecetwo-stroke