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MXA RACE TEST: 2017 YAMAHA YZ125 TWO-STROKE

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Can you teach an old dog new tricks? Not this decade-old smoker. This old dog needs more than a new chew toy. It needs to step into modern times.

Can you teach an old dog new tricks? Not this decade-old smoker. This old dog needs more than a new chew toy. It needs to step into modern times.

Q: FIRST AND FOREMOST, IS THE 2017 YAMAHA YZ125 BETTER THAN THE 2016 YZ125?

A: Yes. For 2017, the YZ125 has improved pucker power. The Yamaha has gone up to a 270mm front rotor from its previous old-school 250mm rotor and has different front brake pads. This is the same rotor and pads off the YZ250F and YZ450F. Other than the front brake, nothing else was improved, unless you count its Bold New Graphics (BNG).

Q: IS ONE UPDATE BETTER THAN NONE?

A: For the last 12 years, the Yamaha YZ125 has been virtually unchanged with respect to performance or handling. We do, however, give Yamaha some credit. True, three out of the last 12 years have only seen BNG, but, in the other nine years, Yamaha made more than one change to the smoker. Most changes were cosmetic, while the other changes were to be in closer compliance with the YZ250F, as well as to conform the YZ125 to a worldwide spec. At this point we are just happy that the YZ125 is still in production. Yamaha is the last of the Japanese manufacturers to produce 125cc and 250cc two-stroke motocross bikes. For that, we are grateful, although we believe Yamaha two-strokes won’t be around much longer if KTM keeps taking Yamaha’s market share. To prevent this from happening, Yamaha will have to make some drastic improvements to its smoker line to even be on par, much less close the gap, with the Austrians.

The small YZ125 powerplant was once mighty for its size, but that time has past, while the Austrian powerhouse has gotten closer to 125cc perfection.

The small YZ125 powerplant was once mighty for its size, but that time has past, while the Austrian powerhouse has gotten closer to 125cc perfection.

Q: WHAT CHANGES DID YAMAHA MAKE TO THE 2005 YZ125?

A: The 2005 YZ125 is the base for the 2017 YZ125. The 2005 engine was all new, sharing only the kickstarter and clutch plates with the 2004 engine. It was smaller, lighter and faster. Yamaha ditched the domed 2004 piston for a flat-top piston. The connecting rod was shortened by 3mm. Yamaha raised the exhaust port 0.5mm and tilted the engine forward 7.5 degrees to straighten the intake tract from 16 degrees off center to 5 degrees. The coolant port on the head was changed because of the engine tilt. The water-pump impeller was changed to plastic, and the drive shaft was made 4mm smaller. The clutch actuator arm was relocated inside the ignition cover. The transmission went from five to six speeds. The exhaust pipe got a straighter initial section.

In 2005 Yamaha switched from its old steel frame to a new plug-and-play aluminum frame. This is virtually the same frame used on the 2017 model. There wasn’t a single round tube on the 2005 frame; instead, it used forgings, castings and extrusions. The 2005 Yamaha YZ125 frame was 4-1/2 pounds lighter than the 2004 steel frame. The bike weighed 197 pounds and got Honda-style brake routing and 7/8-inch Renthal aluminum bars for the first time. The Kayaba forks were copies of Showa’s Twin Chamber forks. We called them “Showabas.” The Showa features the dual chambers, top-mounted compression adjuster and one-piece outer tubes.

2017yz125right

Q: WHAT CHANGES DID YAMAHA MAKE TO THE 2006 YZ125?

A: On the 2006 engine, the shape of the combustion chamber’s squish band was radiused out to the edge of the band. The carburetor got one less bypass port and a new 6BFY42-74 needle. A stiffer power-valve governor spring made the valve open at 9500 rpm instead of 9000 rpm. The ignition got new CDI mapping and an NGK BR9EVX platinum-alloy plug. Back in 2006, Yamaha made a change that still defines all Yamaha’s that came after that year. What was it? They replaced the “Showabas” with Kayaba SSS suspension components. With SSS (Speed Sensitive System), Yamaha’s suspension went from 30-percent speed-sensitive damping to 90-percent speed-sensitive. As for the shock, it was as close to a works shock as any production bike had ever come. It had an 18mm shock shaft instead of 16mm, Kashima-coated internals, a 30-percent-larger reservoir and a titanium shock spring.

Additionally, for 2006, Yamaha added adjustable handlebar mounts, a sleeker front-brake lever, an on-the-fly quick-adjust clutch lever, wider fork-tube spacing, a low-profile rear-brake caliper, new rear-brake pad material, a plastic rear-brake caliper and rotor guards, a softer and taller saddle, a new front number-plate shape, and a Dunlop D756 rear tire to replace 2005’s D739, although the front remained a D739.

To get the YZ125 into the meat of its powerband, the clutch needs to be abused to get there and stay there.

To get the YZ125 into the meat of its powerband, the clutch needs to be abused to get there and stay there.

Q: WHAT CHANGES DID YAMAHA MAKE TO THE 2007 YZ125?

A: Yamaha made five changes to the 2007 YZ125. (1) The fork stanchion tubes were tapered into a thinner midsection and new damping was added. (2) The steel components on the Kayaba shock (spring guide, clevis bushings, rebound clicker internals and compression adjuster) were replaced with lighter aluminum pieces. (3) The 7/8-inch Renthal handlebars were replaced with 1-1/8-inch Pro Taper Contour bars. (4) Aluminum bolts replaced the previous steel bolts on the subframe, engine mounts, seat, side panels, front fender, triple clamps, rear-brake caliper guard and chain guide. The front axle nut was changed to aluminum. (5) The silencer’s perf-core section was shortened by 75mm (with the remainder of the core constructed from non-perforated stinger) to improve throttle response without increasing sound.

Q: WHAT CHANGES DID YAMAHA MAKE TO THE 2008 YZ125?

A: For 2008 Yamaha made eight changes to bring the YZ125 into closer compliance with the YZ250F four-stroke. The 2008 YZ125 got the front-brake caliper, fork stanchions, lower fork bracket and chain guide from the YZ250F. A new reed valve was added. The front master cylinder piston was made 1.48mm smaller, while the brake lever was positioned higher on the master cylinder and 9mm farther from the handlebar.

Don’t let its good looks fool you. Underneath the YZ125’s shiny plastic is a decade-old chassis and engine.

Don’t let its good looks fool you. Underneath the YZ125’s shiny plastic is a decade-old chassis and engine.

Q: WHAT CHANGES DID YAMAHA MAKE TO THE 2009 YZ125?

A: The 2009 YZ125 underwent four changes. (1) Yamaha dropped its oversized, steel, serpentine brake-hose holder in favor of a 32-gram-lighter aluminum clamp. (2) The chain got a special zinc coating. (3) The textured seat cover of 2008 was replaced with a woven seat cover. (4) The D739 front tire was dumped for a Dunlop 742F.

Q: WHAT CHANGES DID YAMAHA MAKE TO THE 2010 YZ125?

A: BNG.

2017yz125silencer

The ultra-long silencer was introduced in 2011. It was an attempt to make one global model, that with new jetting could be sold in lots of countries.

Q: WHAT CHANGES DID YAMAHA MAKE TO THE 2011 YZ125?

A: Yamaha made several changes to the 2011 YZ125 model to make it conform to the worldwide global spec so they could sell the same model in every country. This was a money-saving move, not an improvement. The global-spec changes were limited to a 75mm-longer silencer, with its core increased from 27mm to 30mm, and 71.5 percent more glass-wool packing. Additionally, the 410 main jet was exchanged for a 430, while the 6BFY42-3 needle was swapped out for a 6BFY43-3 needle (the needle and jet came as options in the tool kit in 2010).

Q: WHAT CHANGES DID YAMAHA MAKE TO THE 2012 YZ125?

A: BNG.

Q: WHAT CHANGES DID YAMAHA MAKE TO THE 2013 YZ125?

A: A white rear fender was added, along with Bold New Graphics.

Q: WHAT CHANGES DID YAMAHA MAKE TO THE 2014 YZ125?

A: BNG.

By adding a tooth to the rear, you can make the usable power easier to reach, but that means your left foot will be busy.

By adding a tooth to the rear, you can make the usable power easier to reach, but that means your left foot will be busy.

Q: WHAT CHANGES DID YAMAHA MAKE TO THE 2015 YZ125?

A: Yamaha created buzz with the 2015 YZ125 by putting its emperor in new clothes, so to speak. While it’s true that Yamaha’s two-stroke tiddler received bigger footpegs, Dunlop MX52 tires, the latest-generation KYB Speed-Sensitive fork and a new airbox, the biggest updates were solely cosmetic. That’s not necessarily a complaint, because the YZ125 needed a facelift.

Q: WHAT CHANGES DID YAMAHA MAKE TO THE 2016 YZ125?

A: Black rims, a gold chain and BNG.

Q: WHAT CHANGES DID YAMAHA MAKE TO THE 2017 YZ125?

A: A new 270mm front disc brake (up from 250mm), which also features a new brake-pad material for improved pucker power. This is a nice addition and brings YZ125 braking into the real world. As a bonus, the 2017 YZ125 weighs 194 pounds.

2017yz125hump

Q: IS THE 2017 YZ125 BETTER THAN THE 2017 KTM 125SX?

A: If it didn’t beat out the KTM 125SX last year with the orange bike’s atrocious 4CS suspension, it wasn’t going to win out against KTM’s amazingly effective AER air forks in 2017. The WP 4CS suspension components were horrible. MXA testers couldn’t use the KTM’s power to its full potential, as the forks were either too soft and bottomed metal to metal, or were too harsh in the mid-stroke. That was the past, though. There are no suspension issues for the 2017 KTM 125SX. The KTM 125SX’s combination of great forks, a bulletproof hydraulic clutch, well-modulated Brembo brakes, modern looks and a step-above handling leaves the long-in-the-tooth YZ125 in the dust. All is not lost, though. We still love the YZ125’s Kayaba SSS components.

Q: CAN THE YZ125 STILL BE COMPETITIVE WITH THE KTM 125SX?

A: Yes, indubitably, but not without putting cold hard cash on the line. And, for some reason, the YZ125 went up in price $109 from 2016 to 2017. Yet, the blue bike is still $400 less than the KTM 125SX and $500 less than the clone-like Husky TC125. That difference is cash you can use to buy some bolt-on power that will make a big difference. What hop-up parts should you buy? Here are a few suggestions that will get you the most bang for your buck.

(1) Pipe. For less than $250, you can gain around 2 horsepower with an aftermarket pipe (add in $135 for a silencer). We have had great luck with both Pro Circuit and FMF pipes.

(2) Reed cage. We run a Boyesen Rad valve or Moto Tassinari VForce4 reed cage to broaden the power. The $179.95 Rad valve or $158 VForce4 reed cage are complete replacement reed blocks and valve assemblies.

(3) Cylinder/head mods. A reputable cylinder porter can get more out of the YZ125 cylinder and head for under $500, but it’s easy to tune the YZ’s port timing to a standstill. You could end up with a cylinder that works better holding a door open than on a race bike.

(4) Gearing. Adding one tooth to the rear, going from a 48 to a 49, will perk up second gear, get you to third gear sooner and make the overall ratios between the six gears more user-friendly.

(5) Price calculator. If you are thinking of buying the 2017 YZ125 because it is $400 cheaper than the 2017 KTM 125SX, you might want to add up the mods above to see that your math is seriously flawed.

The one thing we wouldn’t want to change on the YZ125 is the Kayaba SSS forks. These forks are still the best forks on the market hands down.

The one thing we wouldn’t want to change on the YZ125 is the Kayaba SSS forks. These forks are still the best forks on the market hands down.

Q: WHAT DID WE HATE?

A: The hate list:

(1) Chassis. We don’t mind that the YZ125 chassis has flaws. It is a light bike that is well suspended. That can cover up a veritable ocean of little glitches. But, we can’t ignore the fact that Yamaha’s 10-year-old frame numbers give up a lot to KTM’s up-to-date steel frame.

(2) Engine. The clutch has to be abused to keep it in the meat of the powerband. You can buy power, but it will cost you.

(3) Front tire. Dunlop’s less-than-stellar Dunlop MX52 front tire makes the YZ125 front end feel worse than it actually is. Invest in the best rubber possible. Most MXA test riders choose to run a Dunlop MX3S front tire. It works better than the MX52 in most conditions, but keep in mind it wears faster than the MX52. We don’t mind running an MX52 on the rear—if the codition are on the hard side.

(4) Powerband. It’s not that we hate the YZ125 powerband; we just think it needs a little more bottom-end grunt to keep our fingers off the clutch.

(5) Price. The YZ125 may be the lowest-priced bike in its class, but, as the Yamaha sales department has found out, most hardcore YZ125 racers buy used YZ125s and rebuild the engines for under $250. If Yamaha built totally updated YZ125 and YZ250 two-strokes, they would give Yamaha two-stroke riders a reason to buy new. However, as long as the new bike and the old bike are identical, there won’t be any motivated new bike buyers.

2017yz125shockbig

Q: WHAT DID WE LIKE?

A: The like list:

(1) Clutch. We never take our finger off the clutch, and it takes the abuse like a champ.

(2) Suspension. Big or small, Beginner or Pro, the Kayaba SSS (Speed Sensitive System) components are the best suspension money can buy. Lucky for you, it comes stock on the entire Yamaha line.

(3) Maintenance. Anyone who is mechanically inclined can change a YZ125’s top end. A Vertex replica piston kit will cost you $124.48 (www.vertexpistons.com). You could buy two YZ125 pistons for the cost of one YZ250F four-stroke piston.

(4) Bulletproof. Yamaha has the best reputation for lasting durability.

(5) Weight. At under 200 pounds, the Yamaha YZ125 is easy to ride and very agile.

For 2017, Yamaha upped the pucker power to a 270mm rotor. This brings the braking of the YZ125 into the real world.

For 2017, Yamaha upped the pucker power to a 270mm rotor. This brings the braking of the YZ125 into the real world.

Q: WHAT DO WE REALLY THINK?

A: We have loved this bike for decades. It was ahead of its time when it was introduced 12 years ago. It reaped the harvest of its greatness with 125 shootout win after 125 shootout win. But, those days are gone. The Yamaha YZ125 needs a new bag of tricks. Its shining star has been dulled due to the Austrian powerhouse pushing the two-stroke envelope beyond what Yamaha’s pencil pushers are willing to green-light. The 2017 KTM 125SX is better in every way. Twelve years ago, it was the other way around. There’s a new sheriff in town.

This is how we set up our 2017 Yamaha YZ125 for racing. We offer it as a guide to help you find your own sweet spot.

KAYABA SSS FORK SETTINGS For hardcore racing, we ran this setup on the 2017 Yamaha YZ125 (stock clickers are in parentheses):

Spring rate: 0.42 kg/mm


Compression: 12 clicks out
Rebound: 12 clicks out
Fork-leg height: 5mm up
Notes: These are awesome forks, made all the more terrific by the light feel and snappy input of the two-stroke engine. Obviously, if you are fast or fat, you might want to go stiffer on the fork springs. Typically, however, fast riders can dial in more compression—and use the crossover effect of rebound damping to get the stock fork springs to work.

KAYABA SSS SHOCK SETTINGS For hardcore racing, we ran this setup on the 2017 Yamaha YZ125 (stock clickers are in parentheses):

Spring rate: 4.7 kg/mm


Race sag: 100mm (105mm)
Hi-compression: 1-1/2 turns out
Lo-compression: 12 clicks out
Rebound: 12 clicks out
Notes: The shock doesn’t do anything funny or out of the blue. It likes to track straight and be in tune with the bike. We love this shock.

keihincarb

YAMAHA YZ125 JETTING Yamaha has its jetting down, and our 2017 YZ125 ran clean. Why wouldn’t it be, they have had 12 years to iron out the bugs. Here are the 38mm Mikuni TMX jetting specs:

Main jet: 430


Pilot: 40
Needle: 6BFY43-3
Clip: 3rd from top
Air screw: 2-1/4 turns out|
Notes: Yamaha includes one richer (440) and one leaner main jet (420) with the bike. The current 6BFY43-3 needle is a half-clip richer than the old 6BFY42-3 needle used before the global spec came into play. If you port the engine or add an aftermarket exhaust system, consider going up on the main jet (440) or even adding a splash of VP C-12 to every 5 gallons of gas for safety’s sake.

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