Atk 604

ATK 604

CYCLE WORLD TEST

Dual-purpose done right

IF THINGS WERE SIMPLE, DUAL-PURPOSE BIKES WOULD BE A 50/50 proposition, equally at home on the street as in the dirt. Things rarely are simple, though, as the evolution of D-P bikes shows. For the past half-decade, manufacturers, searching to expand the dual-purpose market, gave us bikes with more street features, until most D-P bikes became dirtbike wannabes, with road-oriented suspensions, tires and ergonomics. Lately, we’ve seen a move back towards dirt-biased machines, as exemplified by the Suzuki DR250/350S series and the Honda XR250L, a move we at Cycle World heartily applaud.

Now comes ATK with its 604 dual-purpose model to really muck up the equation. You've always wanted a dirtbike with lights? This is it, a street-legal off-road Th u mper.

Well, make that barely street-legal.

Don't be misled by the lights, turnsignals, provisions for a license plate and DOT-approved tires. True, those items may fulfill many states’ registration requirements, but, in reality, this ATK is identical to its dirt-only 604 EFI counterpart, and may or may not be street-legal in your state.

Why has ATK taken its excellent big-bore Thumper and tacked on street amenities? Does the company intend to do battle with the DRs, KLRs and XRLs of the dual-purpose market? In a word. yes. According to Jack Roten, ATK’s vice president, general manager and part owner, “A lot of people have asked for a street-legal dirtbike. We decided to build a competition bike in a trim that could be made to meet various states' vehicle codes. In other words, a goodhandling off-road bike that you could take on the street."

Like its dirt siblings, the street-going 604 EFI is powered by a hulking Rotax Single. Providing in the neighborhood of 50 horsepower, the air-cooled Thumper measures 94.0 x 8 1.0mm for a displacement of 562cc. As expected, the torquey engine provides effortless firstand second-gear wheelies, and dirt-tracking through your favorite asphalt backroad is only a lean angle and a handful of throttle away. Dragstrip clockings show that the ATK is about a half-second quicker through the quarter-mile than the class’ 1990 speed king, the Suzuki DR650S.

Numbing vibration accompanies that performance, though, with serious vibes seeping through the handlebar, footpegsand fuel tank. This problem is most noticeable in a straight-line freeway situation. Time spent riding backroads and trails delivers so many thrills that the shaking goes all but unnoticed.

As we've noted in previous tests of dirt-only ATKs, the company's electric-start feature is a blessing. Engine hot or engine cold, the starter—powered by a small, closed-cell battery—never faltered. For purists, starting the 604 via the backup kickstarter is possible, but cold starts require a lot of patience and a firm follow-through. Booting a warm engine to life, though, is simple. One or two swift kicks, in concert with the bar-mounted compression release, quickly brings the Single to life.

Next on the we-like list is the new fuel-injection system, which tolerated any amount of throttle in any gear, and yielded a flat-spot-free powerband. The only glitch surfaced with an occasional backfire through the airbox. This problem was later traced to the idle circuit, which was set too low. The somewhat-cobbled airbox fitted to our test bike is a fiberglass prototype, to be replaced by a betterfinished unit on the production bikes.

The exhaust system also will be changed. By the time you read this, a “street” exhaust, a twin-silencer Answer unit, should be ready, hopefully much quieter than the booming off-road pipe our test bike was fitted with. And, yes, the new system will be forestry-approved.

We’d like to see the final gearing raised, too. As is, the 604's gearing is identical to that of its ofi-road counterparts, and is too low for street use. Raising the gearing might lessen cruising vibration, as well. At least the internal gear ratios are nicely spaced. And, around town, thanks to the powerplant's prodigious torque output, the smooth-shifting gearbox can be left in fourth, and even, fifth gear.

A beautifully built, nickel-plated, chrome-moly steel frame houses the powerplant and its associated hardware. The dual-purpose 604 uses the same frame as the enduro 604, which features a more conservative steering-head angle than its motocross-oriented brother.

ATK's suspension components are of premium quality. The latest, multi-adjustable White Power cartridge fork and single rear shock are standard equipment. The fork is adjustable for rebound and compression damping, while the non-linkage rear shock offers rebound, compression and preload adjustments. Both items provide a stiff platform for street riding, but more than make up for their pavement inadequacies when the bike is ridden off-road. Once in their familiar habitat, both ends offer splendid performance, soaking up everything from rocks to potholes to tree roots.

Like the suspension, the 604's braking abilities are best appreciated off-road. A single, 9.25-inch floating rotor and a four-piston Grimeca caliper handle the duties up front. While the brake offers excellent feel and plenty of stopping power off-road, the system comes up short on the street. More braking performance would be appreciated on the street but, in turn, might lead to overkill in the dirt.

At the rear, minimal pedal pressure is required to actuate the twin-piston Grimeca caliper that grips a 5.25-inch countershaft-mounted disc. A foot unaccustomed to the set-up can easily lock the rear wheel and kill the engine. Increasing play at the pedal is a quick cure.

DOT-approved Pirelli Gara Enduro tires provide commendable performance for dual-purpose rubber. The generously knobbed tires are surprisingly sure-footed on asphalt, though they can be persuaded to slide when speeds are upped. In the dirt, both ends offer good traction, but aren't quite up to the abilities of full-on knobbies. Still, as a 50/50 compromise, the Pirellis are just about the best dual-purpose tires we’ve sampled.

Compromise is the name of the game with dual-purpose bikes, and the AI K is no different. Traveling by pavement to and from your favorite fireroads or trails points this out. Street comfort is not the 604’s forte, the blame going to its narrow, rock-hard saddle. In addition, the tall seat height puts the rider on level with most 4X4 trucks, and makes stoplights a tip-toe procedure for riders under 6 feet tall.

Also, several important street-going items were absent from our test bike. Without a horn, a speedometer, a rearview mirror and a toolkit, the 604 is far from a fully rigged roadbike. A I K informs us that the 1992 model, available early this fall, will feature a variety of accessory items, including a speedometer/odometer combo, a longer, wider and softer seat, buddy pegs, a steering lock, a mirror and shorter-travel suspension components. While they’re at it, the guys at AT K would do well to consider adding a horn and a toolkit, especially considering the 604's whopping $7795 price tag, $500 more than the Standard ELI dirtbike.

That price is hard to swallow, certainly, but the ATK’s effectiveness is not. To many riders, this will be a dream dual-purpose bike, one that can roost down rocky trails or down to the corner store. It's also something of a look into the crystal ball.There may be more dirt-biased, electricstart D-P Thumpers in our future. Last year, we rode a prototype Honda, a cobbled-up XR600 powered by an electric-start NX650 motor. Earlier this year, we saw another XR/NX prototype that looked good enough for production. In 1992, we may or may not see the Honda, which would be considerably less expensive than the AI K. And whether the other manufacturers follow suit remains to be seen. What we do know, though, is that the future of big-bore D-P bikes is right here, right now, in the form of the ATK 604.

ATK 604

$7795

EDITORS' NOTES

I’VE GOT A PRETTY GOOD IDEA OF WHAT a dual-purpose bike should be. My YZ-suspended, White Bros.-built Yamaha XT350 offers a darn good dirt/ street combination. Or so 1 thought until this turnsignal-equipped ATK rolled into the Cycle World garage.

I he 604 is so capable off-road that I was skeptical of its street prowess. No worries. True, touring-bike comfort isn't on the ATK’s resume, but in the right hands, this big Thumper will unravel a canyon road with impressive ease, even preying on wide-eyed, sportbike riders in the process. (Don't ask me how I know.)

After riding the 604, I'm selling my XT. The combination of performance and—bless you, ATK-electric starting makes the 604 very tempting. Frankly, though, the near-$8000 asking price is a bit rich for my blood. Maybe Honda's rumored NX650-powered, electric-start XR will have the right combination of affordability and offroad capability. —Matthew Miles. Associate Editor

THIS IS THE DUAL-PURPOSE BIKE THAT A lot of hard-core off-road riders, including me, have been begging the factories to build for years: ninetyfive percent pure dirt racer, five percent streetbike.

That means the 604 EF1 has the raw power and exhaust bark of a real dirtbike. It also has the same frame, long-travel suspension, seat, footpegs, riding position and handling. Who cares if the final gearing is too low for the highway, or the brakes a bit small for serious canyon carving? A short hop to the corner store is exhilarating. and limited distances on paved surfaces can be tolerated if the route leads to an off-road playground.

The 604’s generous fuel tank frees me to explore remote rural areas; its suspension soaks up bumps, and its electric starter instantly lights the engine. But best of all, this bike lets me ride as fast as I want off-road without fear of exceeding its handling limits. Or mine.

—Ron Griewe, Senior Editor

LORDY, GET THIS THING AWAY FROM me. If I spend any more time on the ATK, my driver’s license will have the life expectancy of an Iraqi armored division during the Gulf War. Wheelies? How high and through how many gears? Acceleration? How about top-gear roll-on times on par with a Yamaha FZR1000?

To be completely honest, the 604 isn’t much of a streetbike; there’s still too much enduro racer in it for that. On the other hand, a lot of so-called dual-purpose bikes aren’t very happy off-road. I recently spent a soggy hour-and-a-half unsticking a BMW R100GS and a Honda NX650 from the unyielding clutches of a gooey jeep trail. Both bikes had ground to a halt when their lowmounted, street-oriented front fenders packed with mud and locked the front wheels as effectively as a gorillagrip on the brake lever.

The lesson to designers of dual-purpose bikes? If you’re going to err, err on the dirtbike side of things. Just as ATK has done. —David Edwards, Editor