Duncan Racing has a reputation for building race ready quads that hold up to the abuse and wear and tear of competition. Long time west coast ATV racer Doug Eichner has won the World Four-Stroke Championships, held at Glen Helen Raceway in Southern California, aboard a modified Duncan Racing Honda 400 EX for the last two years running.
This feat was particularly impressive because Doug did it using an air-cooled, Single Overhead Cam (SOHC) four-stroke engine that is admittedly a good decade behind the latest crop of Double Overhead Cam (DOHC) liquid-cooled four-stroke motors.
How did he do it? Some of it, of course, has to do with Doug’s skills as an ATV racer, but even the best racer has to have a machine that he knows is capable of winning. Doug’s Duncan Racing modified Honda EX was built to put out a broad spread of power and engine torque that makes riding the air-cooled Honda engine at warp speed extremely easy.
Instead of having Duncan make him a mega-horsepower, wheel spinning, wheelie-prone monster motor, that would, in Doug’s opinion, make the machine even more difficult to ride, he had them build him an engine that gets all the available power to the ground instead of focusing on high peak numbers.
To do that, Duncan built up a stock 2002 Honda Fourtrax 400EX with one of their 440 “National” engine kits. It includes their newest Fat Boy 4 exhaust system, a 440cc piston kit (installed), a ported cylinder head, valve job and shortened bronze valve guides, a high performance cam shaft, heavy duty valve springs with titanium retainers, an Edelbrock carb kit, K&N air filter, and Outerwear filter cover. All for a total price of $2250.
This particular engine kit is designed to give the EX a much broader and stronger hit without making it unrideable or unreliable. They claim a 40-50 percent increase in horsepower over the stock Honda’s numbers (from 27 hp to around 40+ hp). With an increase in horsepower, a beefed-up clutch was also necessary. A DR C-128 set of clutch plates were installed with new clutch springs inside a Hinson Racing clutch basket. To make clutch changes easier, a DR quick change clutch cover was also installed. A new Tsubaki 520 O-ring chain replaced the stocker with a set of 16/36 teeth front and rear sprockets.
Check out the detailed specs at the end of this story for more complete information on the prices of these performance engine, drivetrain, clutch and suspension modifications.
FAST TRACK RACER
One of the first things we noticed about the Duncan 440 EX was how cleanly detailed and good looking it was. Duncan Racing prides itself on building quads that are race ready and look the part. They only use the best aftermarket products available and the fit and finish are as important as the overall performance.
The Duncan quad was set up to race long distance events, such as Grand Prix and fast desert races, where smooth, controllable power and plush suspension are prime considerations. It was also built to be extra comfortable for extended trail rides. To facilitate this, it had a Roll Design LOBO II front suspension kit with Elka shocks with 10.75 inches of travel up front and an Elka rear shock with 11 inches of travel on a Roll Design swingarm on the back end. A 49-inch wide Dominator rear axle replaced the stock Honda unit for a more stable rear end to match the wider Roll front A-arm (50 inches). This combo makes the EX chassis extremely stable in rough terrain and much more capable of full throttle runs through the whoops.
Douglas aluminum wheels and ITP Holeshot knobbies where shod on the front and back ends of the machine (21×7-10 fronts, 20×11-8 rears) to get the power to the ground. A set of TAG T2 CR high bend handlebars and a Duncan Racing anti-vibration handlebar clamp were also installed for comfort and control on the machine. A set of aluminum OMF skid plates were mounted front and back to provide extra protection for the engine, chassis and swingarm and a Duncan Racing chrome front bumper gave the front end a leaner, racier look.
To improve footgrip, a set of Roll Design cast stainless steel footpegs with kick up ends were installed. Custom engine guards were also built into the frame for added protection against rock damage. A large capacity IMS fuel tank (4.5 gallon) replaced the stocker for increased range for long distance riding.
In the braking department, a set of Crown series steel braided brake lines with BRAKING pads and rotors were installed on the front and back ends of the 440 EX for improved braking power and feel.
OTHER BITS AND PIECES
Some of the other items added to the quad included a Motion Pro CR twist throttle and cables, Scott grips, Honda CR clutch perch and lever, a Hinson Racing billet rear brake pedal, DR billet shift lever, a GBR steering damper, Pro Design kill switch, DR nerfs, One Industries graphics kit and seat cover, and an Ace high capacity oil tank.
TRACK AND TRAIL TESTS
We borrowed the Duncan Racing Honda 440 EX and raced and trail rode it for several weekends to see for ourselves how well this hand-built racer performed. Was it as good a race and trail machine as Doug Eichner claims it is? Or was his superior riding skill the reason he made winning on it look so easy?
Well, the answers are yes and yes. With the Duncan National engine kit, the air-cooled Honda 440cc kitted motor does put out a sizeable increase in overall power. It is not “rip-your-hands off the bars” kind of power, though. It comes on early and strong but the overall impression is a smooth and steady rush that revs out on the top end. The Fat Boy 4 exhaust system cranks out a healthy mid-range hit that makes riding the EX even easier. You can shift early and let it pull a gear high coming out of a corner. We liked the smooth feel of the Hinson clutch and how well it held up to the abuse we heaped upon it. Our brakes had a much more solid feel and sure action with the new steel braided lines and heavy duty BRAKING pads and rotors.
But the area we were really amazed with was how well the revamped suspension performed. Thanks to the LOBO II front suspension kit with its Elka front shocks combined with the Elka rear shock and Roll Design rear swingarm, the EX chassis was literally transformed.
You could now charge through the roughest whoops flat out, with no hint of swap or bottoming out whatsoever. With the increased power available from the Duncan Racing engine kit, you could take full advantage of it, anywhere, at any time, on the track or trail.
There wasn’t a single situation where we felt we couldn’t fly through the worst terrain we encountered without ever having to back off the throttle! Now we know why Eichner can keep the throttle fully pegged when he’s on the toughest parts of the course. It certainly is confidence-inspiring when you know you can barrel through a whoop section or off a steep jump without having to back off the gas.
That is one of Doug’s secrets to going fast. The other is that he has the skill, endurance and talent it takes to keep it operating at this frenzied pace from start to finish.
Overall, we have to give Duncan Racing and Doug Eichner credit for making the Honda 400EX a competitive mount against the newest unslaught of high performance quads threatening Big Red. It all goes to show; if you spend enough money, and have the heart and skill of a champion, anything is possible.