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Yamaha XT 600
You can't help but feel sorry for dual-purpose motorcycles. They've become trapped in a world they never built, saddled with a jack-of-all-trades, master-of-none role in an era of ever-increasing specialization.
It wasn't always this way. Back in the old days, there were no such things as specialized motorcycles, or even dual-purpose motorcycles. In effect, every bike was an a//-purpose machine. You took the lights off of your street bike and stripped some weight if you wanted a cowtrailing machine. If you took off even more weight, hopped-up the engine and put on the appropriate tires and handlebars, you had either a road racer or a scrambler. And a touring bike? Well, that was the same basic street machine with a duffel bag strapped to the rear and some sort of aftermarket, handlebar-mount windshield up front.
Just like those bikes of yesteryear, today's dual-purpose motorcycles can do just about anything. It's just that they suffer anytime they're compared, one category at a time, to any of the specialized bikes. Yes, some dual-purpose machines can be used for long-distance touring, but compared to gliding along the highway on one of the big touring bikes, doing so is an ordeal. Off-road, a good rider can take a dual-purpose bike almost anywhere, but an equally skilled rider on a proper dirt bike will get there sooner with less effort—and fewer crashes. On twisty backroads, dual-purpose bikes account for themselves amazingly well, but a good sport bike remains a far better choice for doing Kenny Roberts imitations.
Still, dual-purpose motorcycles seem to maintain a small but loyal following of riders who believe in the one-bike-for-all-uses concept. And the prestige class for dual-purpose machinery is the big-bore division, bikes that displace from 500 to 600cc. Yamaha's entry in that category is the XT600, a 595cc thumper that can trace its lineage back to 1976 and the TT/XT500 models, the first modern reincarnation of the classic large-displacement, single-cylinder four-stroke.
As Yamaha's dual-purpose flagship, the XT has all the latest tricks. Styling, of course, is heavily biased towards the dirt side of things, which is apparent in the high-mounted plastic fenders front and rear. A red, motocross-style "safety seat" sweeps forward onto the gas tank to cushion a rider's delicate parts. The sidepanels and headlight cover have blacked-out panels meant o resemble number plates. There's a tool pouch mounted on the rear fender just like on the real enduro bikes. There are even air shrouds attached to the bottom of the gas tank, which seems a trifle gimmicky, although Yamaha claims they direct cooling air to the engine. But it's hard not to believe that the black plastic shrouds are there to resemble radiator shrouds. And, in fact, quite a few observers asked, "Water-cooled, eh?" as they gave the air-cooled XT a quick once-over.
There are other, non-gimmicky components on the XT600, like the open-cradle frame that closely resembles the one used on the dirt-only TT600. A substantial aluminum skid plate in the classic coal-shovel pattern protects the bottom of the engine from rock damage. The front fork assembly has 41mm stanchion tubes (down 2mm from the TT600's), air caps and 10 in. of travel. An impressively strong front disc brake easily hauls the 600 down from highway speeds yet is still controllable enough for effective use in the dirt.
Yamaha went all-out on the XT's rear suspension. Gone is the 550's old-style Monocross system that placed the shock in an almost-horizontal position above the engine, replaced by a lower-mounted shock and a link system that provides for progressive springing and damping rates. The bottom link pivots, as well as the swingarm pivots, have grease fittings, while the top pivot, where the shock attaches to the link, is protected from wheel-thrown debris by a pleated rubber boot. The shock itself is adjustable for both spring preload and rebound damping, and the adjustments are easily made at the lower end of the shock. Rear wheel travel is 9.3 in.
A nice touch is the aluminum box-section swingarm, lighter and better looking than the customary silver-painted steel unit. The arm pivots on needle roller bearings. Snail-cam chain adjusters and a quick-detach rear wheel make chain-tightening and tire-changing duties easier.
Power to move the XT down the road or the trail is provided by an engine that follows the modern thumper pattern. A single
overhead camshaft opens and closes four valves via rocker arms. Exhaust-valve size, 31mm, is one millimeter larger than on the 550 engine, but the engine's 84mm stroke is the same as the 550's. The 600's added displacement comes from increasing the bore to 95mm. The compression ratio is 8.5:1, the same as on the XT550.
As a weight-saving measure, Yamaha fitted the XT with a chrome-plated aluminum cylinder liner (the same as on the TT600) instead of a more-conventional iron liner. We've heard reports that some TT cylinder liners get out-of-round easily, causing oil consumption to go up. Some TT600 owners even have resorted to installing iron liners. When asked about the problem, a Yamaha spokesman said out-of-round liners and oil consumption shouldn't be a problem if the bike is broken-in carefully.
Instead of a single exhaust header pipe, two smaller pipes exit the cylinder, curving to the right before merging into a larger-diameter pipe that leads to a heavy-looking (but quiet) muffler under the right sidepanel.
Like most of today's big four-stroke Singles, the XT uses a dry-sump oiling system, which requires a separate oil tank. But instead of using a frame tube or backbone as a reservoir, the XT600 has a metal tank hung off the left side of the frame, tucked underneath the sidepanel. Yamaha explains that this type of oil tank was used to help achieve a lower center of gravity (the XT550's oil is carried in the backbone above the cylinder head), and to keep the hot oil away from the steering head, where it shortens bearing life. We never had any problems with the tank on our test bike, but an XT owner who rides a lot in rocky terrain would be well-advised to keep an eye on the tank, since it can easily get punctured by a fall onto a sharp rock.
The XT600 uses a dual-carburetor setup, dubbed YDIS for Yamaha Duo Intake System. Most dual-purpose and off-road four-stroke singles now use some kind of dual-carb system, the theory being that at low rpm, where one large carburetor doesn't mix fuel and air very efficiently, a smaller carburetor will give better throttle response. At increased rpm the secondary carb kicks in to give the engine the fuel it needs for higher speeds. The XT's carbs—a 27mm slide-type primary linked to a 27mm CV-type secondary—are manufactured by Teikei. Most of the time they worked just as the theory dictates, although, there were instances when the engine would stumble, almost as if the secondary carburetor was taking a gulp before getting on with its job. The condition was especially annoying in passing situations on crowded freeways. Before reaching any firm conclusion about the performance of the carburetors, we cleaned and re-oiled the dual-stage foam air filter. This helped—it seems the new XT has inherited the TT600's trait of easily clogged air filters—but a slight hesitation was still there, between 4000 and 5000 rpm.
Hesitation or no, the carburetors metered fuel to the engine very efficiently. On the Cycle World mileage loop the XT returned 61 mpg, giving the bike nearly a 180-mi. range from its 2.9-gal. gas tank. The Yamaha usually went on reserve between 140 and 150 mi.
Carburetion also played a part in the way the big XT started—easily for a 600cc thumper, which is not to say easily compared with most motorcycles. First off, there is no electric starter, since a kick-only design is more in keeping with the bike's off-road, less-weight theme. There is, admittedly, an automatic decompressor that opens the exhaust valves when the kick starter is depressed, but it still takes a healthy kick to get things moving. In the morning it's best to use full choke with no throttle, and the XT will rumble to life in three or four kicks. The bike can be ridden away immediately with the choke still on, since no warm-up period is necessary—a pleasant change from the cold-blooded way many four-cylinder street bikes behave.
When warm, the XT will fire with just one kick .. . usually. There were times—two or three during the 1400-mi. test pe-
riod—that the XT just refused to start. Kicks, curses and push-starting had little effect. After a few minutes rest and some more kicking on the part of the rider, the XT would spring happily into its 1500-rpm idle.
Once started, the engine is a joy. Around town, shifting at 3500 rpm (redline is 7000 rpm) and letting the bike lug its way around corners seems to work best. So with its generous suspension and torquey engine, the XT makes the ideal urban commuter. Potholes, cobblestones and all other normal road hazards don't bother the bike in the least.
Out on the open road, things change a little. Even with the XT's gear-driven counterbalancer and rubber-mounted handlebars, for instance, the rider can feel vibration; this is, after all, a big Single. The vibration doesn't really intrude until the bike is running along at 60 mph, but from that point on the XT shakes in earnest. Not bad for short blasts down the highway, but an Interstate tour at 70 mph will have the rider wishing for something smoother.
Better to stick to two-lane backroads with lots of dips and twists and places to stop and enjoy the scenery. But those stops are almost mandatory, thanks to the hard seat. Thin on top to allow for non-bow-legged standing on the pegs in the dirt, the seat just doesn't offer much support. Fifty miles has the rider shifting his weight around and 100 non-stop miles is a true accomplishment.
Handling-wise, the 600 is nimble in terms of street maneuverability but, naturally, not the most agile dirt bike on the market. But for a bike that can do both kinds of riding, the XT is quite competent. The only handling quirk we did notice was that the bike steers heavily and sluggishly at low speeds. And the culprit is the OEM front tire, a new-pattern Bridgestone Trail Wing. For a dual-purpose tire the Bridgestone has a really aggressive tread design; it would be fair to call the tire a semi-knobby rather than a typical trials-universal dual-purpose design. The tire worked nicely on the street and got surprising traction in the ment we fitted a more conventional Dunlop dual-purpose tire and effected an instant improvement. Even riders who thought that the XT hadn't handled all that heavily with the stock tire noticed a lighter front-end feel with the Dunlop.
Regardless of tire choice, however, the XT makes an excellent off-road explorer. It will splash through streams, climb impressively steep hills and slide around smooth turns at a good clip. On a fire road a talented rider can really hustle the XT along. But, at 318 lb., the bike can become a handful through
rough sections in a hurry. Pushed hard, sooner or later, the weight or lack of real off-road suspension and tires will catch up with the XT; and dumping a heavy bike at the speeds the 600 is capable of is a sobering (and slowing) thought.
Granted, as with any dual-purpose motorcycle, the XT has its limitations both on the street and in the dirt. But that assessment really isn't fair. If you're looking at what a dual-purpose bike won't do well, then you've missed the point. Better to look at what the bike will do; and in the XT600's case, that's just about everything.
Source Cycle World 1984