First Tests: 2005 Yamaha YZ125 and YZ250

When Yamaha first shocked the world with its all-new and extremely innovative YZ400F and then a few years later with the YZ250F, many industry insiders were claiming this was the beginning of a slow and painful death for the two-stroke. As most of the manufacturers jumped on the four-stroke bandwagon over the last few years, it seemed two-strokes were being overlooked. Then rumors began flying out of the Land of the Rising Sun that Yamaha was putting tons of emphasis on its two-stroke lineup for 2005. The first spy photos of the '05 YZ models proved the tuning-fork company was not cutting any corners with its premix-burning bikes. From that moment on, the same question kept coming from everyone's mouth: Why put so much time into a two-stroke?

"We set the precedent with the four-strokes, and now we want to have the best two-strokes. We want to see two-strokes on the track; we sure don't want to see the two-stroke phased out of closed-course competition racing. We will continue to develop two-strokes, and we have no plans of letting up on our two-stroke lineup," Yamaha's silver-tongued PR guy Terry Beal said. We couldn't have said it better ourselves, and we hope he's right!

The '05 YZ125 is truly a new bike from the ground up, with the YZ250 seeing the same major chassis and suspension changes. These two redesigned YZs could really throw a curveball to the consumer when it comes time to buy a new bike; once again, two-strokes could be back in demand.

YZ250

We'll start with the engine. It's thin on new features, but the YZ mill didn't need much. It got a heavier piston, a new pipe and a totally redesigned countershaft sprocket. Crisp and fresh, our test bike ran as strongly as any YZ250 ever, if not just a bit crisper. Yamahas have had plenty of power lately, and it is the same story here. If anything, the engineers just bookended slightly more throttle response on the bottom with a little more overrev on top. Not to worry, as the Yamaha has that throttle-to-rear-wheel connectivity other 250s are seeking. When you twist your wrist, the power makes the rear wheel do what you want it to do. A little throttle gives you the control and tractability you'll need in slippery conditions or on timing obstacles. A serious twist yields the boost you'll require to shoot out like a cannonball with all the muscle the Dunlop 739 can handle.

With a well-spaced and tight tranny, there's a gear for everything, and missing shifts isn't a concern. The clutch takes plenty of abuse—mostly in controlling power, not in trying to search for more. It is just a bit heavier than what we'd call a one-finger pull, but it is still light. We ran the standard jetting from sea level to 3000 feet, and it was tack-sharp; so much so that, running on pump gas, the Yamaha begins to detonate just when you set the throttle in turns or just as you put the motor under a heavy load. Then it promptly cleans up and rips—just like the finely tuned race machine it is. Some of our riders were looking for more overrev in the deep loam of RaceTown 395, but no one complained about outright power. If there ever were a two-stroke that could be ridden in one gear, this bike would be the closest, but it still can't match a four-stroke in that respect.

The chassis—made from aluminum and 5 pounds lighter than last year—accounts for the huge weight drop. Right off the bat, you notice the machine is lighter; it has a distinctly less-top-heavy feel than before. In fact, the bike is not top-heavy at all anymore. Now the 250 Yamie is easy to throw into turns, especially tight ones. The initial effort required to lay in the bike takes noticeably less muscle. And when you want to get the bike over a bump or settled in a turn or make adjustments to flight plans, it is easier to move it up and down through the handlebar. It just plain responds, as does the 125.

The front fork has been a sore spot with YZ owners for a while now, so Yamaha should have painted the new ones bright red to ensure everyone would notice them. Very similar to works forks internally, the separate air-oil system provides damping control comparable to that of a shock with a true closed system, eliminating any air bubbles that would make for inconsistent valving. It also gives better control through the whole stroke. This allowed Yamaha to soften the initial part of the stroke to be more compliant, whereas before it was stiff to keep the bike from blowing through the stroke. Now the 250 has a supple feel, more like a Showa-equipped bike. The mid-stroke is still pretty soft, so it plunges a little. Then the fork ramps up in progression, but it doesn't bottom nearly as hard or as frequently as it did before. We did bottom more than we liked with our faster riders, so we added 7cc of oil and eliminated that problem. Then we were able to run even less compression damping for a plusher feel. We didn't have to fiddle with the rebound at all.

Meanwhile, the shock drew little attention. It was supple like the fork and plush even on sharp hits, plus its bottoming resistance was just right. Again, we didn't feel the need to change from standard settings. But what has become a bit more critical is the ride height: You can feel the difference in a few millimeters, and it pays huge dividends in steering. We ranged between 100 and 110mm of sag, depending on how much the rider liked a planted front end, and it never hinted at any instability. Although we weren't cursed with any horribly rough tracks, the 5-pound-lighter bike danced just a bit more than in the past. But none of our riders had any unsettling moments while riding.

Both YZs have great brakes that are as strong as anything but also give great feel—especially the front. Bonus for the nice lever. Aluminum bars make the ride that much better and save you one step in setting up the bike properly. The titanium footpegs are too nice to just be stomped on all day long, but that's what they're there for. And the new plastic is supposed to white out less, yet it still does.

If Yamaha was trying to make an aluminum-framed bike that doesn't feel like an aluminum-framed bike, it succeeded. None of the riders noticed any traits that shouted out, "Hey, I'm not steel!" It's just as good as ever—lighter, but still as potent. Plus, with the new fork leading the package, this bike is really a contender.

YZ125

Although we've seen many factory Yamahas with aluminum frames in Europe and Japan, this is the first production YZ sporting the alloy. After some serious R&D, engineers were able to come up with a well-handling aluminum chassis and, in the process, shed almost 5 pounds compared with last year's steel skeleton while still managing to keep it durable. The new aluminum frame is truly a piece of engineering art featuring cast, forged and extruded pieces for the best balance possible. This process allows the frame to avoid the perceived ultrarigid feel of aluminum. We lucked out and were able to test in extremely gnarly conditions (two weeks without grooming) at Glen Helen Raceway Park. Straight up, the YZ125's chassis offers a ton of feedback; it's easy to tell what the bike is doing at all times. Still, we thought the frame had a slightly stiff feel to it over square-edged bumps under acceleration. This makes setting up the suspension for your weight more important than on past years' YZs due to the large reduction in flex. Another key ingredient to the chassis is the changes that were made to the swingarm. It is now 42mm wide, 5mm up from the '04 YZ, giving the bike a more-stable feel and allowing it to track much better out of corners. Plus, the new swingarm weighs a little more than a pound less than last year's.

At first glance, the new Kayaba fork looks as if it's right off one of the factory Yamaha race bikes, less the trick coatings. The fork has some big changes for '05, with the most important being the new air-oil separation system. A transfer control valve is now submerged in the fork oil at all times, making the fork speed- and stroke-sensitive. The cartridge tube and rod use a Kashima coating along with a new oil seal, resulting in less friction. The new fork uses a stiffer spring rate: 0.42kg/mm compared with 0.41 for '04.

We saw noticeable performance gains on the track. The improvements to the fork gave it a much more-progressive stroke compared with the previous year's unit, which inspired rider confidence. We're happy to report that the fork's harsh, head-jarring, metal-to-metal bottoming-out sensation is gone. Our test riders felt more confident on flat landings off big jumps right away. The new fork soaked up anything in its way and was very progressive. It's also very tunable; it took only a few clicks to stiffen it when we tested at a very smooth Perris Raceway. Typically, the stock settings were near-perfect for most of our testers.

Out back, the Kayaba shock also got a good going-over. The biggest and most-noticeable improvement is the full rebound oil-lock system, which helps control the damping at the beginning of the stroke and makes the shock more progressive. It also helps with less top-out on the shock. As with the fork, the shock spring rate was bumped up, from 4.5kg/mm ('04) to 4.7 ('05). Under acceleration, the shock complements the new frame, as it allows the rear tire to track straighter than before and is very predictable. This new more-progressive shock, as with the fork, soaks up big landings better without loosening your brain. We played around with different ride heights and found that most riders preferred running about 100mm of sag.

Visually different from last year, the '05 YZ125 motor grabs your attention. The cylinder sits angled in the chassis 7.5 degrees farther forward for performance gains resulting from a straighter intake tract, which greatly improved throttle response. A more-compact design everywhere, the motor weighs 4 pounds less than last year's powerplant.

On the track, the new mill is very impressive. Last year's engine lagged big time off the bottom-end, and we found ourselves changing gearing trying to make up for the lack of power. The new version has a much more-solid roll-on from the bottom and, as it did last year, really comes to life in the midrange, where the power pulls hard! Not stopping there, the YZ builds into a decent top-end with plenty of overrev. Yamaha's stock jetting worked decently, only a little rich on the bottom. We were able to do some fine-tuning and cleaned up the bottom-end. We ran the 6CHY6-80-4 needle (one-half clip richer than the stock 6CHY5-80-4 needle) and a 35 pilot jet (from the stock 40). In '04, we had a tough time keeping our YZ from going flat on top. Some of this was due to unmatched transmission ratios and the higher gearing we needed to put on it to pull off the bottom. Now, the '05 YZ returns to a well-matched six-speed transmission that is spaced more closely between gears. Gone are the gaps that the bike didn't have the power to pull through. Therefore, it's much easier to keep the motor singing in the high-rpm range throughout all the gears. The new setup blows away the old five-speed. Plus, not only is the new six-speed transmission good for the track but now the YZ125 is much more rider-friendly if you opt for a trail ride.

YZ250 OPINIONS

The Yamaha YZ250 definitely feels as if it's a new motorcycle. The aluminum frame offers a ton of stability and is super-compliant. I noticed a big difference in the frame, as the center of gravity feels much lower and the bike turns anywhere, anytime. I loved the way it felt in tight corners. I could flick the bike really quickly with no effort at all. In the air, the YZ flows and goes where you tell it to go. Although all is good while riding, I'm tired of the way it looks. I think it's time for a change in the bike's wardrobe, as the same old blue is getting boring.
Corey Neuer/5'11"/165 lb/Intermediate

What I really noticed about the YZ125 was that it corners exceptionally well; the same goes for bigger brother YZ250. These bikes are absolute fun in loamy dirt corners. The 250 two-strokes have always left me struggling with endurance because their power is so abrupt and they are a little heavier than what I'm used to riding. Thanks to the smooth roll-on power of the YZ250, I didn't feel as though I struggled a bit; I felt I used a lot less energy riding the bike. The suspension worked fine and I felt very confident jumping; the bike felt very stable and predictable—OK, maybe it's a little stiff for my liking, but I didn't get enough time on it yet to work out the fine-tuning.
Joe McKimmy/5'9"/155 lb/Novice

More 250 two-stroke motocross bike tests:

2005 Kawasaki KX250
2005 KTM SX 250
2005 Suzuki RM 250

YZ125 OPINIONS

After reading about the all-new YZ125, I knew it would be fun on the track. The bike is amazingly light; it feels the same way my downhill mountain bike does. The weight savings feels huge on the track, and I love the way the YZ turns with ease. In rough conditions you can really pick and choose your lines, and it is really easy to change lines midway through a corner. Thanks to the weight loss, you can really ride the bike; I didn't feel as if it were riding me, even when I was tired. You just pick a line, and the bike sticks. The new motor is way faster than last year's. It has some much-needed bottom-end along with incredible mid and top-end power. The new six-speed transmission makes the bike easier to ride; I never found myself searching for power while shifting gears, as the new tranny is very well-matched from first through sixth. The new YZ125 is a ton of fun, but I did get tired more quickly on the 125cc two-stroke than I did on the YZ250F four-stroke. When it comes time to line up at a starting gate, I think I would still choose the four-stroke for the fact that I could run the same pace all the way through a moto. My first few laps may be faster on the 125, but I think I'd tire out too quickly as the 125 requires more effort to ride hard.
Corey Neuer/5'11"/165 lb/Intermediate

I spent a lot of time switching between the 2004 YZ250F and the 2004 YZ125, mainly because the YZ125 felt so light and easy to maneuver—and this is even more so with the 2005 YZ125. I instantly noticed how much lighter the bike felt than the '04. The motor felt very strong and smooth throughout the powerband, and I loved the crisp snap of the low-end power. The bike also didn't feel as finicky about what gear I was in, as the '04 125 did. The suspension felt very good all around. I really liked how plush the front end felt off big landings, and the bike seemed very stable in the rough areas of the track. The handlebar was a bit high, but this was easy to adapt to. All in all, I really liked the bike even compared with last year's YZ125. But if it came down to choosing just one of the 2005 bikes, I am not sure I would give up the 250 four-stroke for the 125 two-stroke.
Joe McKimmy/5'9"/155 lb/Novice