In case you've slept away most of the year, we'll fill you in on a couple of updates. A kid by the name of Ricky Johnson came a breath away from winning the National Championship on what is purported to be a… (we'll pause for a moment here, clear our throats, and emphasize that we can't verify this)… a stock bike.

We can vouch that RJ's bike appears to be essentially stock—a production YZ250J just like the one we've tested, just like the one you can buy. In any case, after we got Johnson to model for us it became perfectly clear, he admitted, that his bike didn't feel much like ours because ours wasn't suspension-tuned to his weight and riding style. We'll buy that; in our testing of the bike it was apparent that proper setup is crucial. Tune the YZ's suspension properly and it performs on par with a properly tuned Honda or Suzuki (which are, we might add, also sensitive to proper setup, especially the Honda). But tune the YZ merely close to what's right and you'll be bouncing around the track, wondering what went wrong.

The point is—if that makes you think that winning is more than ever a matter of precision refinement (not only the bike but your body), you're right. In its particulars, the YZ has what all the major contenders have: water-cooling, a double-leading-shoe front brake, a rising-rate rear suspension system. The catch is, for the Yamaha, the designs are newly implemented. The YZ's liquid-cooling and rear suspension linkage system come a model year after Honda introduced its, and a year after Suzuki developed its Full Floater. Which means the other two companies have had exactly one year longer to refine systems in several ways.

The YZ250J is a complete redesign of the air-cooled YZ. The chassis, suspension components, engine, body work and seat are all new, and they work together to make the J-model considerably better than the 1981 YZ-H.

The most notable change to the YZ concerns its engine. Although the lower-end is basically the same as last year's, the modifications from the top of the case halves up are substantial. Liquid-cooling, though new to the 250, is nothing Yamaha hasn't had experience with, proof being Yamaha's success with liquid-cooled road racers.

The system used on the 250J is almost identical to the one on the 1981 YZ125H. The fork-mounted radiator, which rests in front of the top and bottom triple clamps, is protected from most damage by the combination number plate/shroud. It is made of a fairly thick plastic with strengthening ribs moulded in. To avoid the problems of routing hoses from the frame to the fork assembly (which must, of course, turn continually), Yamaha utilized the frame's front downtube, steering head, steering stem and top and bottom triple clamps as coolant carriers. Hot coolant, fresh from the cylinder assembly, flows through a hose to the back of the steering head. From there, it passes into the steering stem, through the top triple clamp, out a small connecting hose and into the top of the radiator. The coolant then makes its way through the radiator, out the bottom through a hose similar to the top one, through the bottom triple clamp, into the bottom half of the steering-stem and steering-head a rea and down the front frame downtube. A hose carries it to the water-pump impeller, where it is pumped through another hose to the front of the cylinder head.

The YZ's system, an efficient design, uses less external plumbing than either the Honda or Suzuki. However, it has drawbacks. The radiator, though reasonably light, increases steering inertia because it mounts several inches from the steering axis. Also, a small crack anywhere in the coolant-carrying frame members cannot usually be repaired in the field, unless, of course, you have a welding outfit handy. On the other hand, a leaky hose can usually be temporarily repaired with a quickie tape job.

Yamaha engineers used their roadracing background to develop another key feature of the new engine—the Yamaha Power Valve System. YPVS is Yamaha's unique method of widening the powerband by altering the effective height of the exhaust port while the engine is running. The duration that the exhaust port is open affects both a two-stroke's powerband and the power output. It's a rule of thumb that an exhaust port with a high ceiling results in a peaky engine with a narrow powerband.

Peak horsepower is where it's at in motocross—up to a point. Mid-range is important, too, and trends really determine how much mid-range people will sacrifice for peak power, and vice versa.

"Rick Johnson has won a few Nationals aboard his YZ250J, a production bike purported to have few modifications. With the proper preparation, your YZ should be equally capable. "

With YPVS, Yamaha is attempting to compete with the high peak-horsepower competition and give us mid-range, too.

The mechanics of it are straightforward. The flat-sided cylindrical Power Valve is located at the top of the exhaust port. To increase its effectiveness, Yamaha located it as close to the actual port window as possible. Riding on bushings, the valve's various degrees of rotation are determined by the Power Valve governor, which is located behind the right-side case cover. It receives its drive through a pair of crankshaft-driven gears. The Power Valve governor is a simple device which operates via centrifugal force. Four steel balls are encased in a machined cup with small, ramped guides for each ball. A spring-loaded retainer directly opposes the cup. As rpm increases, the balls are thrust outward from the center of the cup. The concave shape of the cup forces the retainer away. The retainer works against its spring and slides along its supporting shaft, which in turn moves a grooved washer with a small forked lever straddling it. The forked lever, after a series of twists and turns, translates its sliding into rotation of the Power Valve. It is a clever bit of engineering and requires little or no maintenance. With the Power Valve, low-end power (below 4000 rpm) is very good, and the transition from low- to high-rpm power is substantially subdued.

The iron-lined, aluminum cylinder bolts to the cases with four short studs, doing away with the old system of four long studs running from the case to the top of the cylinder head. The cylinder-to-head mating surfaces don't use a gasket; instead, Yamaha relies on two 0-rings to maintain the separation of combustion gases and coolant. To help prevent cylinder-head distortion, Yamaha securely fastened the head to the cylinder with six six-millimeter studs.

Although the YZ's engine has a new exhaust method, little has been changed on the intake side. A new sidecover / number plate has eased airbox access; you have to remove only one Phillips screw to get to the two-piece oiled-foam element.

The round-slide 38mm Mikuni carburetor feeds its mixture into a new thin-petal reed valve. The intake port has been re-contoured with a dip across the top extending down into the port. Presumably, Yamaha wanted to give more support to the intake side of the piston skirt throughout the piston's stroke.

The geared primary drive no longer uses helical gears. Although the new, straight-cut gears do create more noise than the smoother-running helical-type, on a motocrosser, who's to notice? The advantage is, of course, that straight-cut cogs are more efficient than helical.

Overall, the YZ250 looks similar to its bigger brother, the YZ490J. Some critical dimensions, such as wheelbase, rake and trail, differ slightly, but the basic chassis design guidelines are the same.

Yamaha's rising-rate suspension, the most recently refined version of Mono-cross, retains the familiar shock beneath the fuel tank. From there, it is substantially different. A new, flat, extruded aluminum swing arm replaces the old triangulated type. Wheel movement, and hence swing-arm movement, is transmitted to the shock through a lever and frame-mounted bell-crank assembly. The new aluminum-bodied monoshock provides adjustments for spring preload and rebound damping as before, and now includes adjustable compression damping as well. The rebound adjustment ring is readily accessible at the rear of the shock. Tuning the compression damping requires that the front of the fuel tank be unbolted and raised out of the way. Spring preload is by threaded collar. The nitrogen reservoir bolts to the right side of the front downtube.

Yamaha's motocross bikes have always had excellent fork assemblies, and this year's YZ is no exception. The stout 43mm tubes keep flex to a minimum, and special internal bushings practically ensure stiction-free travel. Black rubber gaiters cover each tube and offer two advantages: Dirt-free seals last longer and, because all dirt is kept out, stiction-causing fork wipers are unnecessary. Air caps are fitted to each leg, but in keeping with the times, Yamaha recommends running zero psi air pressure.

Front and rear brakes have been carried over from last year's H-model. In an effort to chop some weight off, Yamaha made the front and rear actuation arms forged aluminum. The rear brake torque arm is likewise made of a light alloy and replaces the heavier steel units. Rear brake actuation is by cable.

Cold-starting and warm-up require the starter enricher knob (choke), but in a short 20 to 30 seconds the engine responds to normal carburetor circuitry.

The YZ's abundant low-end and smooth power delivery are probably the first things you'll notice about the 250. It doesn't have the bottom-end grunt of a trials bike, but in the low-end it's the most tractable 250cc two-stroke motocross bike we've ridden.

If you ride 250s in a fashion similar to the way most people ride 125s, you will probably rarely notice the benefits of the YPVS. At high rpm, the YZ feels much like any other 250. If, however, you let the YZ fall off the powerband and ride away without the usual clutch fanning, you'll find that the low-rpm power is strong enough to pull you back into the heart of the powerband easily and quickly. That's nice when you find yourself in one of those predicaments where all you can do is twist the throttle.

After spending a few hard laps on the YZ, the next thing you'll notice is weight. On paper, the weight difference between the Yamaha and other 250s seems insubstantial. The YZ is 5.5 pounds heavier than the Honda CR250R, and 12.5 pounds heavier than the ultra-light Suzuki RM250Z.

But gross weight isn't the whole story—weight distribution plays at least an equally important part—and the fact is that the YZ feels distinctly weighty compared with the CR and RM. Off jumps, for instance, if you don't land dead straight, the YZ skitters and slides.

Like all modern motocrossers, getting the YZ set up for a particular track and rider is crucial if you want to get the most out of the bike. Various spring options for the shock along with 24-way rebound and 10-way compression damping make tuning the YZ complicated. But it's worth it. A couple of clicks on the damping adjustment and a modest preload change affect the chassis' dynamic attitude and can make the YZ handle much better for your weight and ability.

The YZ-J, even though it has a new chassis, displays many familiar Yamaha handling characteristics. It's neutral all around the track, and steers impressively well. The front end sticks in all but the tightest turns, where the bike can feel somewhat cumbersome. Straight-line stability is good, much better than last year's YZ over rough sections. In sand, the YZ works great. Turning is a snap, and the front tire rarely pushes.

The Monocross suspension rates considerably above the old system. But, as we noted in the YZ490J test (Cycle, April 1982), the progression curve is a touch abrupt. The first half of the travel is a tad soft; it feels as though the rear suspension is riding halfway through its travel at all times. It doesn't affect the steering, but it takes some getting used to. The final half of the travel needs refinement too; it feels firm but bottoms occasionally. Both front and rear brakes work well. The only moto cross front brake that works better is Kawasaki's disc setup. The YZ's drum brake, though, is still excellent, with a nice, linear response at all times. The rear is equally good, without any over-sensitivity to locking.

Yamaha's redesign of the YZ keeps it at least in the running for top motocrosser honors. The YZ is yards ahead of the H-model 250 and close to the other 1982 motocrossers. We'd like to see Yamaha do two things: rid the YZ of seven to 10 pounds and recalibrate the rear suspension progression curve slightly. That, we hope, is for 1983, and the need for refinement is a predictable result of Yamaha's being a year late to jump on the bandwagon to produce a production-line rising-rate rear suspension system. On the plus side, the YZ's power is excellent, its steering precise, and the potential is there to get the bike into the winner's circle, even at a National Championship race.

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Hannah's '82 Factory OW was run "Air Cooled" after just a few short races. Bob thrashed his "Water Pumper" in disgust with a hammer. 1982 would be the last of the "Hurricane" in yellow, as he would jump ship to the Factory RC's at Team Honda for '83. The saga of "HURRICANE II" would soon begin in "Hannah Fashion"!

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