Yamaha Yz250
YAMAHA YZ250
So this is why Yamaha wants to race production motocrossers
CYCLE WORLD TEST:
Yamaha’s Racing manager, Kenny Clark, surprised everyone when he announced the Yamaha factory works motocross bikes would be modified production bikes during the ’84 season. Sure we thought, we’ve heard that one before just before they rolled out the $50,000 works wonders. Just after Clark’s announcement, Ron Lechien won a CMC sponsored Supercross race in San Diego, California. He was riding an ’84 YZ250 he bought from a local dealer two days before the race! Cylinder porting was the only modification, Yamaha said.
No, the 1984 YZ250 isn’t all new. Instead, the ’84 is a highly refined ’83 YZ. But in this case refinement means more than different decals and paint. Refinement means new hubs, forks, shock, rear suspension leverage ratios, frame, tank, seat, pipe and silencer and cylinder porting, plus a host of small but significant improvements to reduce trouble spots encountered on the ’83s.
The hubs are the most radically changed. While most manufacturers are tooling up for (or already have) hubs with straight-pull spokes, Yamaha has come up with something really different, called Z-spokes. Z-spokes get their name from the bend they make in the hub’s flange (see drawing). Each spoke is about twice the length of a regular spoke because they don’t end at the hub; instead they make a tight Z-bend at the hub flange and continue to the opposite side of the wheel, ending at another spoke nipple. Thus, each long spoke has two nipples and no mushroomed end. Yamaha claims the Z-spoke design is stronger, reduces flex and removes stress from the hub. Wide aluminum rims with hollow rim beads are carried over from ’83.
Hard-riding pro motocrossers had frame breakage problems with the ’83 YZ250s, so the ’84 frame is stronger. The front downtube and main backbone tubing have thicker walls. And two aluminum stays are used between the top rear of the head and the frame. The frame’s geometry and general shape are unchanged. KYB forks with 43mm stanchion tubes and 1 1.8 inches of wheel travel are stock. For ’84 they have aluminum damper rods and adjustable compression damping. Other adjustments include air pressure, oil volume and weight.
Rear suspension gets more change. A new vertically-ribbed aluminum shock body dissipates heat better so the oil doesn’t overheat and the shock body doesn’t distort. A remote reservoir has a compression damping knob on its end (20 adjustments) and the rebound damping is altered by turning a knurled knob on the bottom of the shock body (21 adjustments). The Mono-X levers are aluminum and the progression rate is once again slightly changed. The aluminum swing arm is slightly longer than before.
The water-cooled engine looks the same. Internally, much is different. The cylinder porting is totally new; there’s an additional intake port just above the regular one and two additional exhaust ports, one on each side of the main port. Yamaha’s Power Valve System (YPVS) that changes the exhaust port timing to match engine speed is still used but it has been modified. It has two extra exhaust ports that line up with the extra two in the cylinder. A six-petal reed valve controls incoming gas from the 38mm Mikuni carburetor. Other internal changes are designed for better durability: the primary drive gear (on the back of the clutch hub) and the kick start gear behind it are a single unit, not connected by dogs as before; the waterpump shaft spins in bushings, and 3rd, 4th and 5th gear ratios have been lowered to eliminate the lag between 2nd and 3rd.
Plastic parts on the YZs have been fragile for a couple of years; a different, more flexible plastic is used for ’84. And the light yellow color has changed to a darker yellow that almost has a green tint. There’s a new, larger airbox for the umteenth year in a row, and this time Yamaha has actually made it significantly larger. Inside there is a larger oiled foam air filter that’s removed from the left side of the bike.
Sitting on a new 250YZ instantly tells you the bike is a lot different; the ’84 is much narrower at the seat/tank junc-> tion. Last year’s YZ felt like a desert bike with a fat gas tank. The ’84 is nice and narrow. Hand controls, pedals and bars are properly shaped and comfortable.
The YZ250 is an easy starter, hot or cold. The kick start lever is easy to use and the internal kicking ratio is good, making the lever easy to push through while spinning the engine several times per kick. No engine vibration is noticed as the water-cooled engine warms to operating temperature. Blipping the throttle tells the rider this engine is extremely responsive. Dropping into first or second doesn’t produce clanks or other signs of distress and the bike doesn’t lurch. Easing out the easy-pulling clutch, the engagement is positive but not grabby or sudden. The YZ moves swiftly away and the rider has to shift sooner than he expects. The transmission ratios are very close, which means you’re not in any gear very long. The closer ratios and more powerful engine have eliminated the lag between the upper gears, and the stepped powerband of past models is gone; ’84 power is smooth and constant. Power is plentiful from idle up to top revs with no flat spots or surges. This engine is excellent. Well, almost excellent. The transmission has perfect ratios but the actual shifting, something YZs and ITs haven't done well for several years, is awful; the pretty aluminum shift lever is short and the shifting mechanism isn’t as good as the competition’s. The YZ shifts hard. This is bad. Motocrossers require constant shifting under racing conditions. The YZ shifts so poorly the rider is always aware of it, and he shouldn’t be.
Handling is exceptional; the forks and rear end follow the bumps without jolting the rider and swallow the bad bumps and landings smoothly. Steering is positive and neutral; not too quick or too slow, just in between a Honda CR250 and last year’s YZ250. It’ll turn without a lot of effort but it doesn’t dive inside as easily as a bike with a 26° or 27° head angle. It doesn’t shake its head on high speed bumps or scare the rider when blasting through deep whoops either. It’s a nice center-of-the-road approach.
Yamaha’s YZs had the first truly powerful front brake. The dual-leading shoe stopper has been around for some time but the ’84 version is stronger and more progressive, thanks to a new cam ratio. The rear brake is just as good; it’s strong, progressive and not grabby.
The YZ250’s handling can best be described as well-balanced. The front of the bike stays on the ground under acceleration but can be lofted when needed, and the bike doesn't try to loop when jumping.
Our test bike didn’t break or require modification to be comfortable and competitive. The carburetor jetting and the standard suspension settings were fine for most riders and conditions straight from the shipping crate.
If you’ve been wanting a new YZ250, this is the year to buy one the ’84 YZ250 is the best YZ we’ve tested for several years. Get one now before they are all gone, good models go fast.
$2429
