PROJECT ATV: DUNCAN RACING YAMAHA WARRIOR

Pro-level motocross and off-road riders turn to Duncan Racing International (DRI) to build championship-winning machines, but DRI doesn’t only develop engine and suspension packages for 450 race quads. They’ve got a wide range of upgrades for most popular sport ATVs, and all the parts are tested with the same concern for performance and reliability as those for the most serious competition machines.

We wanted to see what Duncan Racing could do for the popular Yamaha Warrior 350 without spending too much. Since the Raptor 350 shares the same engine as the Warrior, the mods on this project machine work for the Raptor too. If you want to build an ultimate Warrior 350 or Raptor 350, DRI has engine and suspension kits to raise the performance to much higher levels.

EXTRA ENGINE PERFORMANCE, ECONOMICALLY
One of the simplest, least expensive routes to extra power is a less restrictive exhaust and intake paired with a high-performance cam. Duncan Racing’s Fat Boy 4 complete exhaust system is lighter and far less restrictive than the stock system. It adds power when used by itself and complements the results of additional engine mods. DRI’s Pro Flow air cleaner kit includes a larger, high-flow filter with a mounting flange that seals more positively than the stock filter. The project Warrior we worked with had seen very little use, so the engine didn’t need to be rebuilt, but DRI offers stock bore and big-bore kits for engines that do. For this machine, we chose DRI’s “All Around” cam. It boosts midrange and top-end power without taking away the 350’s smooth low-end power, and it can be used with the stock piston.

HANDLING AND COMFORT
Tires are an important part of sharpening any machine’s performance and handling, so DRI replaced the Warrior’s tall, soft stock tires with STI Tech 4 XCs. These low-profile, six-ply tires flex less under cornering side loads and offer much better flat resistance than the stock tires.

The Warrior handlebars and vibration level needed work, so we had DRI do the repairs with high-performance parts that would improve the machine’s feel. Stock Warrior handlebars have an awkward bend, so DRI replaced them with shock-absorbing Flexx handlebars with a more natural bend. Flexx handlebars act as part of the machine’s suspension system by absorbing shock in the same plane as the suspension while offering solid, direct steering control.

DRI replaced the stock steering stem with a Roll Design Anti-Vibe stem. The rugged, race-proven stem is made with light, strong chromoly steel. Antivibration bar mounts calm the buzz from the Yamaha’s engine. A GPR steering stabilizer dampens the jolts, bumps and ruts sent through the steering. It’s fully adjustable for high-speed and low-speed resistance, so you can tune it for the terrain and steering feel you prefer.

RIDING IT
The Yamaha Warrior and Raptor 350 have torquey, tractable power, but they can stand a shot of excitement. DRI’s simple and affordable cam, intake and exhaust upgrade gives the Warrior the snap and high-rpm power it lacks without forfeiting its easy-to-ride power delivery. Added power actually makes the Yamaha easier to ride, because the engine pulls harder and longer in each gear, which makes gear choices less critical.

When our affordable Warrior project started, we wanted to see how much we could improve its handling and comfort without the expense of new shocks. DRI provided three solutions: STI Tech 4 XC tires, Fasst Flexx bars and the GPR steering stabilizer. The tires don’t increase comfort, but they are an important handling upgrade for this machine. The sturdy six-ply construction and low-profile design noticeably improve the Warrior’s cornering feel. Together, the bars and stabilizer are in the price range of a new pair of front shocks, but each offers a big improvement in the machine’s feel. The Flexx bars cut vibration and suspension harshness. The GPR stabilizer calms bump steer, which makes the Yamaha smoother and easier to control. If cost is an issue, you can start with either one and add the other later. The best thing is, you can transfer these parts to your next quad or any quad you ride.

ENGINE:
Fat Boy 4 Complete Stainless Steel Exhaust System: $499
DR H2 Camshaft “All Around”: $179
HD Valve Spring Kit w/ Titanium Retainers: $135
Pro Design Pro Flow Air Cleaner Kit (Foam): $99

CHASSIS:
DR Chrome Front Bumper: $199
Roll Design Anti-Vibe Stem: $349
Flexx Handlebars: $349
GPR Steering Damper w/ Mount: $449
Crown Series Front Brake Line: $119
Crown Series Rear Brake Line: $39
DR Billet Throttle Cover: $49
RK XW-Ring ATV Off-Road Chain: $99
DR Block-Off Plate: $15
Alum Rear Grab Bar: $49
Works Connection Clutch Perch Assembly: $149
STI Front Tech 4 XC 22x7x10 Tires
STI Rear Tech 4 23x10x9 Tires