Yamaha TT 250

Road Test 1980

Don't let the TT250 fool you. It might have a Monoshock rear suspension and a leading-axle fork like its YZ cousins, but it was never intended for the motocross track. Tucked behind the combination number plate and refreshment canteen are 242 pounds of fun, because the TT250 is a playduro for winning smiles, not trophies.

The secret to winning those first-place grins is a package that contains just the right balance of horsepower, suspension travel and weight for performing tricks in the dirt. So when you screw on the throttle you don't have to worry about an earthshaking amount of torque quickly consuming a small amount of suspension travel and catapulting the whole heavyweight business into a gut-shaker of a crash—the usual sequence of events with 500cc fun-thumpers. The TT250 is one playbike that delivers all of a four-stroke dirt bike's virtues with few of the drawbacks. So after a full day of sliding along dusty fireroads, dodging snags or laying knobby tracks on the wide-open spaces, you're always a winner, even if you don't come home with a trophy. All that remains is to load the TT in the back of the pickup, then stop at the pizza parlor to spend a couple of hours of bench-racing with your dirt pals.

It's clear that the TT250 isn't a race bike as soon as you swing a leg over it and take to the saddle. No motocross bike sits low enough these days to allow you to plant both feet solidly on the ground, but the TT does. In fact, its seat height measures slightly more than 33 inches, about the same as on many street bikes. And what you gain in seat height isn't lost to Ground Clearance, either. Slightly less than a foot of daylight shines beneath the engine's skidplate, elevating the TT250 to nearly motocross standards in this respect. It's one of the best compromises of low seat height and adequate Ground Clearance ever made on a playduro.

Just as low seat height is one of the measures of a good playbike, so too, low overall weight plays an important role. Yamaha has met the challenge without the compromises apparent in the Honda XR250, Suzuki DR370 and Suzuki DS-series. The Yamaha weighs less than 250 pounds dry partially because unlike other four-stroke playbikes, plastic has been substituted for metal wherever possible. The gas tank, number plates, side panels, fenders, seat base and countershaft sprocket cover are all plastic, evidence of a concerted weight-reduction program that makes the TT250 easy to fling around corners and over jumps. As a result, the TT250 is one of those rare motorcycles that lets you spend your off-road time learning how to ride the dirt, instead of learning how to ride a dirt bike.

The TT250 might be a lightweight motorcycle, but the heavyweight punch of the 250cc four-stroke engine is what really makes the package work. It cranks out about a horsepower or so more than the Honda, enough to help this little white tornado scoot across the dirt quick enough to produce a respectable rooster-tail. Better yet, though, the Yamaha engine is torquey, producing good power with far fewer rpm than Honda's engine. There's plenty of power available for getting out of trouble at low rpm. That's the way a playbike four-stroke engine should be—and the way that so few are.

Although the extra torque is present at the rear wheel, the single-cylinder engine operates smoothly, thanks to a single gear-driven counterbalancer. Yamaha chose one vibration damper, as opposed to two normally used on four-stroke singles, to keep total engine weight low. And besides, claim project engineers, one was all this engine needed.

Most of the technology inside the TT's engine is relatively conventional. A 30mm Mikuni slide/needle carburetor without an accelerator pump feeds a single intake valve. The intake and exhaust valves are operated by a single overhead camshaft that rides on needle bearings for long life. In an effort to keep engine height low, the dimensions of the cylinder are extremely oversquare, 75.0mm by 56.5mm. Other features of the engine keep height down as well. For one, the wet sump is shallow (Yamaha decided against a dry-sump configuration like on the TT500 because the necessary oil tank would raise the bike's center of gravity). Another aspect of the engine that reduces the bike's height is the fact that it's used as a stress-carrying element of the frame, so there's no need for frame tubes underneath the crankcases.

The reason for this emphasis on low engine height, of course, is the presence of Yamaha's Monoshock rear suspension strategy. A short IT-style Monoshock connects the mild steel tubing of the swingarm to the mild steel frame. It has a body made of steel like the IT250 shock, too, rather than the sophisticated aluminum now used on the YZ racers. The mono's dual-rate spring has a preload adjustment at the top, which means you must remove the gas tank to get at the adjuster nut. Also, the damping rates aren't adjustable, though the nitrogen pressure of the de Carbon- type shock body can be changed to alter damping rates slightly.

Aside from the special effects required in the engine-height area, the airbox also is the scene of numerous alterations and compromises to make life possible for a Monoshock above a four-stroke engine. Finding a place for it was no easy task, since the shock lives right behind the car- buretor. Yamaha engineers therefore wrapped the airbox around the shock in a complicated and restrictive shape. And to reduce costs, the same airbox shape is com- mon to both the street-legal XT250 and the white tornado, which means the baffles used toquiet intake noise on the XT also strangle the TT's horsepower production, although a different inlet for the TT-style airbox attempts to solve the problem.

Simplicity was the keynote in the kick- starter, for Yamaha didn't want to force the TT250's riders to be seasoned thumper freaks before they could start the single while stranded on the side of a rock-strewn hill. Complexity held the answer, though, for the TT250's kickstarter incorporates an automatic compression release. As the kick lever swings down, a cable-operated compression release cracks the exhaust valve open for about a quarter of the piston's stroke—just long enough for you tout sufficient momentum into the crankshaft to fire the engine without having to leg it with the strength of a rugby layer.

We encountered a serious problem with the compression release, though, because it persistantly malfunctioned. Many times it held the exhaust valve open so the engine wouldn't run no matter how many times you kicked it. The culprit was the bell crank down by the kickstarter, which kept binding in its hole in the primary case. The same problem appeared with our XT test bike and, so Yamaha says with virtually every early XT and TT250. A ser- vice bulletin has been issued to correct the problem and Yamaha has since made improvements. We just disconnected the ca- ble to the compression release and had no trouble starting the engine whatsoever, demonstrating that the device might be fine for the novice rider, but it's really not a necessity.

Once into life, the TT engine settles into a lumpy idle, quietly popping away. Don't sneer at the mild-mannered exhaust note though, despite the fact that sometimes the sound of the suspension working will drown it out. There's plenty of eager acceleration available from this 250cc pop gun, thanks to its flat torque curve. So power is delivered to the rear wheel in gentle, predictable progressive doses. You're never surprised by a rear wheel that suddenly breaks traction, as with pipey two-strokes and some four-stroke cannons. The Yamaha 250's powerband is calibrated to keep the rear wheel hooked up. Traction is its byword. Sure, it has many of the characteristics of a 500cc four-stroke single.

You can fool the carburetor and make the engine die with an erratic wrist and there's a definite punch behind every power stroke—but they're in half-scale proportions. As a result, you've got just the right amount of power to keep you moving in the slow stuff and still scale the incline to the top of Thumper Hill.

Once you're at the top of the hill, though, you probably won't look forward to coming back down. Not because the view is so spectacular but because the brakes are so weak. The front lever in par- titular feels spongy, and there's little reaction until you've grabbed a big handful., Maybe because Yamaha figures the compression of a four-stroke engine will furnish lots of whoa-power, it's equipped the TT with brakes of the slow-you-down variety more appropriate for motocross bikes than the stop-you brakes that you need on the play-trail.

The suspension can be just as soft and spongy, too, because it's built for the relaxed pace of play riding, helping you ride over just about anything that can be conquered while you're parked in the saddle— as long as your speed is not too fast. Spring and damping rates are as well-balanced as the rest of the motorcycle—just keep in mind that the TT isn't for aggressive dirt riders. Comfort, not speed, is the prime directive here.

This is not to say that the TT250 is fit only for plonking around camp, though. Actually it takes to fireroads with relish because it's extremely stable on well- graded dirt and gravel. The fairly high center of gravity due to the Monoshock gives the bike slow, predictable reactions that help it track straight. As a result, the TT is as slick as white lightning on logging roads, farm roads or any piece of winding level ground. You'll feel like a flattracker, for it's easy to induce a full-click slide just by shutting off and pitching the bike side- ways. Even riders without an AMA Expert license can have slideways fun on this bike.

With so much weight high in the chassis, Yamaha has tried to adapt the bike for tight stuff with fairly quick steering geometry like a motocross bike. But the enineers were less successful here. Sure, the g

TT steers precisely and the high CG keeps the bike from feeling twitchy at speed, but you'll feel clumsy dodging cowpies on the tight trails simply because the high center of gravity is the predominate factor in the turns. With proper throttle control you can keep the bike upright and scoot the rear wheel around a hairpin with a blast of power, but otherwise you'll want to use a loot to balance. Of course, the TT250's low seat height helps you put your foot down effectively in the tight corners—it's only motocross-style seat heights that have made us forget how handy a dab can be in the right circumstances.

You'll notice that the number plate actually holds about a quart of liquid refreshment so you can pack your favorite thirst quencher when you're heading for good times aboard the TT250. But you're not going to want to waste precious time chugs-lugging by the side of the trail. You'll want to keep the 250cc single humming over all kinds of terrain, because this bike is made for grinning. In fact, it's the best of the 250cc four-stroke dirt bikes. Sure, the KLX has a sophisticated chassis, but the engine's low calorie count keeps you from having as much fun as you'd like. The XR250, on the other hand, has too much weight, not enough power and a grabby clutch that makes trail riding a nightmare. The balance of motor and chassis makes the Yamaha TT250 the best in its class, virtually unsurpassed as a fun-chaser.

The TT250 gives you the highest grins per-gallon rating of any four-stroke dirt bike you can buy. Sure, popping wheelies, jumping logs, dodging pucker bushes and strafing jeep trails may not seem heroic next to the kind of weekend riding that Mike Bell does on his Yamaha racer, but his fun lasts only 40 minutes. And it takes him hours of training each day just so he can compete in two motos on Sunday. Your riding schedule is just the opposite—you'll spend about an hour prepping for a whole weekend of fun. And after a day or two of cutting through mud puddles, planing over the sand or slaloming through the trees, you'll feel like a winner, too. Because there are no losers on TT250s.

RIDE REVIEW

Those level-eyed, Deadly Serious Dirt Guys might scoff at the TT250's non-motocross performance, but not me. I've sat by too often watching Taylor and Dewhurst performing two-wheeled dirt tricks to miss out on a good thing when I see it. Here, finally, is a device for the sole purpose of making fun-lovers like myself look good in the dirt. What do you want? Wheelies? Powerslides? Or maybe just a fast barrel race through the pucker bushes? Whatever, with the TT you just set the dial for the appropriate stunt and wait for it to happen.

But they don't understand. They keep talking about Winning and something called a Trophy-Or-Die. Even now they're planning to pump up the engine and suspension to make a Real Dirt Bike out of the TT. Fat chance. They'll have to pry me out of the saddle first.—Larry Works

 Half of my ideal 250cc playbike lives here—the engine half. The TT's counterbalanced four-stroke single is smoother, torquier and light-years faster than the boat anchor that propels Kawasaki's sweet-handling KLX250, and it's just as smooth and a bit peppier than Honda's XR250 motor. But for me, the chassis comes up considerably short of acceptable. I like to go fast on the rough and difficult trails, not on the smooth and easy ones, but doing so on the TT bottoms the suspension so loudly and frequently that the clanging of fork and Monoshock often drowns out the exhaust.

That's why I'd love to yank the TT's terrific engine from its low-tech location and splice it into a KLX250 chassis. With a best-meets-best combination like that, I'd have the four-stroke 250 funbike that everyone has promised but none so far have delivered.—Paul Dean

Despite the TT's YZish styling, it is more for the rider whose mental ignition is turned on by the thought of miles of twisty trails and megatons of wet rocks.

Even though I'm one of those riders who is more at home on a motocross track than plonking over hills, I still enjoyed the TT. It had just enough power to crest almost any hill, while running slow enough to keep me out of trouble. But though the powertrain is up to the task, the suspension falls short by about three inches. Ruts that other bikes swallowed whole and spat out the exhaust pipe gagged the TT, sending through jolts that measured 6.5 on the Kidney Scale. Riding the TT will never replace busting berms on a YZ, but it isn't supposed to. It is supposed to be a playbike, and someone looking for that kind of machine won't have to look any further than a TT250 Yamaha.—Dean Taylor

GETTING SERIOUS WITH THE TT

The TT250 isn't just a la bike. For fans of four-strokes and manufacturers of accessories for dirt bikes, it's the best news from Japan since Yamaha's TT500 in 1976. Sure, it's intended to entertain the casual cow-trailer, but the bike is so good it's going to find itself in more serious hands as well. As a result, the TT250 looks set to take over from its bigger brother as the most modified and tweaked-upon dirt bike around.

For good reason, too, because within the limits imposed by soft suspension and mild engine tuning, this Yamaha 250 shows more potential for speed than any other four-stroke bike. A strong motor with plenty of untapped horsepower is one reason, but what makes the difference is the fact that the bike is compact and light for a four- stroke. Even in stock form, this quarter-liter thumper could hold its own in enduro competition, not because of any single brilliant feature, but due to sound overall design. It won't bury a Husky 390 on fire roads or smoke a KTM in the tight stuff, but because it has enough of the right things—enough horsepower, enough suspension, enough competition bike-caliber handling—it can keep you within your enduro hour and possibly help you stay on your minute. Only the new generation of enduro bikes can really humble the TT250 on the trail.

Help is on the way to make the TT250 an even more serious competitor, thanks to a cavalry charge of high- tech artillery from the accessory companies and even Yamaha itself. Ed Scheidler of Yamaha's competition ser- vices has worked with the bike and discovered that a Monoshock spring from the YZ250F with a free length of 304mmgives the TT's rear suspension the racer's edge. Similarly, a fork spring from an IT175G in each fork leg plus 15cc more stock-weight oil will keep the fork from crashing to full compression at every bump. You can also use air caps from the YZ125D and pressurize the fork legs to 4.3 psi for extra help.

The accessory companies, mean- while, are at the ready with lots of hard- ware. Pro-Tec offers air caps and an aluminum swingarm, while White Brothers offers the same plus a conversion for the fork that delivers 10 inches of travel. Yet even though the suspension parts are being manufactured, it's the engine that fascinates the after- markets. White Brothers has discovered through dyno work that dispensing with the airbox adds two horsepower while using a replacement exhaust pipe adds two more. Poweroll and Pro-Tec also offer a pipe for the bike, and Pro-Tec points out that its replacement pipe saves 13 pounds over the stock piece.

All the other usual horsepower mods are waiting in the wings for the TT250 as well, including 34mm Mikuni or Dell Orto carburetors and radical cams. The usual route to large herds of ponies, though, is through big-bore kits. Because the TT250 engine is so over- square, this strategy promises problems in the form of acute rod angles and high piston speeds, but Pro-Tec, White Brothers and Poweroll each market big- bore kits. Pro-Tec has a 350cc conversion, while White Brothers' 270cc bore kit probably represents a less radical solution to the problem.

Whatever displacement they happen to be, however, just about every TT250 that turns a wheel will have at least one thing in common: They will be modified in one way or another. That's be- cause the TT250 holds far more potential for speed than the TT500 thanks to good handling and light weight, even though Yamaha has set the bike's limits fairly low. By setting your own limits with pieces from Yamaha and the after- market companies you'll find that the TT250 is one of the most serious four-stroke dirt bikes in history.—David Dewhurst

Source Cycle Guide 1980