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MXA RACE TEST: THE REAL TEST OF THE 2020 YAMAHA YZ125 TWO-STROKE

Q: FIRST AND FOREMOST, IS THE 2020 YAMAHA YZ125 BETTER THAN THE 2019 YZ125? 

A: Let’s not beat this subject to death. Everybody should know by now that the Yamaha YZ125 hasn’t had any major updates since 2006. There are pluses and minuses on the YZ125’s ledger sheet because of its length of duty. The plus is that the YZ125 has had such a long lifespan that most of the known flaws have been found. There are no YZ125 surprises. The big minus is for the lack of R&D. The competition hasn’t sat on its hands over the YZ125’s 14-year technology drought. 

Given that Yamaha has done very little to improve the powerband, peak power or torque on the YZ125 engine, the horsepower gap is where the YZ125 really falls short. This is a fun bike to ride, but in stock trim it is not a fun bike to race. It needs more power, because by its very nature every 125cc engine starts life at a disadvantage to other bikes on the track. But, Yamaha’s horsepower deficit is more grievous because every engine tuner on the planet can get 37 horsepower out of the YZ125 engine, even if he uses the standard operating procedures from 14 years ago. The question isn’t, “Can the YZ125 be made more competitive?” The question is, “Why hasn’t it been?”

Q: HOW DOES THE 2020 YZ125 RUN ON THE DYNO? 

A: If you’ve ever ridden both the YZ125 and KTM 125SX back to back, your seat-of-the-pants dyno should have told you that the YZ125 is actually better than the Austrian 125 from 5000 rpm to 7800 rpm. The YZ125 picks up quicker and cleaner on the exit of turns. A YZ125 racer is less likely to flub getting back on the pipe than a KTM 125SX racer; however, when you are talking about 125cc engines, you are rarely talking about how great they are in a part of the powerband where the engine is at its weakest. If you think that running better below 7800 is a resume filler for the YZ125, you have your powerband priorities backwards.

All 125s, dating back to the formative days of 125 two-strokes, are ranked by how they run above 7800 rpm. These have been, and still are, wide-open powerbands. The term “on the pipe” was created just for 125cc two-strokes. And when the Yamaha YZ125 and KTM 125SX are on the pipe, the YZ125 comes up lacking in the horsepower department.

Let’s break it down. At 7800 rpm, where the YZ is at its best, the Yamaha is 1/2 horse better than the KTM; however, by 8000 rpm, when the 2020 KTM 125SX powerband comes on the pipe, the Yamaha is down 1/2 horse to the KTM. By 9000 rpm, the Yamaha has given up 2 horsepower to the KTM, and when the two engines reach peak power, the KTM is making 37.50 horsepower, while the YZ125 is only making 33.52. Which would you rather have? A 125 that works great below 8000 rpm or one that works best above 8000 rpm?

Q: HOW MUCH TORQUE DOES THE YZ125 HAVE?

A: The 2020 Yamaha YZ125 makes its peak torque at 11,000 rpm. It produces 16.29 pound-feet of torque. The 2020 KTM 125SX makes 17.69 pound-feet of torque.

Q: HOW DOES THE 2020 YZ125 RUN ON THE TRACK? 

A: If you own a YZ125, don’t ever throw a leg over a KTM 125SX. Why not? It will cost you a lot of money, because you will not go back to the Yamaha after feeling the top-end power on the KTM. Paradoxically, while not as powerful or as fast, the YZ125 is a blast to ride. The added dose of power down low makes it easy to get the blue bike up to speed with nary a touch of the clutch. And while it may not match the KTM’s numbers at high rpm, it does rev to 11,700 rpm before falling off the pipe. From the saddle, you don’t feel any flat spots or dips in the powerband. The engine is always connected and working hard. What it lacks in hyperkinetic high-rpm power, it makes up with a filled-in powerband that allows the rider to get on the gas sooner and use what it has to offer to its fullest.

Q: WHAT DOES THE 2020 YAMAHA YZ125 COST?

A: The 2020 Yamaha YZ125’s manufacturer’s suggested retail price (MSRP) is $6599. Not surprisingly, the retail price of the 2020 KTM 125SX is $7299. The price difference between the Yamaha YZ125 and 125SX is $700.There is a large segment of the off-road world that is looking for a time-tested, reliable, solid performing dirt bike, and that bike is the Yamaha YZ125. It has been honed over the last 14 years

Q: CAN YOU MAKE THE YZ125 COMPETITIVE AGAINST THE KTM 125SX?

A: The $700 you save by buying the Yamaha over the KTM could be used to get the 2020 Yamaha YZ125 up to par, horsepower-wise, with its orange nemesis. Here is a complete list of where to find power.

(1) Pipe. For $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 and $168 VForce4 reed cage are complete replacement reed blocks and valve assemblies.

(3) Porting/head mods. A reputable tuner can get more power out of the YZ125’s cylinder and head for under $500; however, getting maximum power may require race gas.

(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. You can find sprockets for under $50.

(5) Miscellaneous. Don’t spend a penny of the $700 on suspension, wheels, titanium, graphics or other foof. Spend every cent you have on power. On a small-displacement bike, power trumps suspension, handling, braking, clutch performance and turning. Although all these things make for an improved bike—and you can’t discount the KTM’s better clutch, stronger brakes, updated handling, hydraulic clutch, great shifting and chromoly chassis—they won’t matter as much if you can make your YZ125 super fast. Note that the 2020 KTM 125SX is as modern as a 125cc two-stroke gets. You aren’t going to make the YZ125 modern for $700. 

Q: SINCE THE 2006 MODEL, WHAT HAS YAMAHA UPDATED ON THE YZ125?

A: Here is a short history of Yamaha’s updates over the last 14 years.

2006: The best thing that Yamaha’s engineers ever did to the YZ125 was to spec Kayaba SSS suspension components in 2006. 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 shock has ever come. It had an 18mm shock shaft (instead of 16mm), Kashima-coated internals, a 30-percent-larger reservoir and a titanium shock spring. 

2007: In 2007 the YZ125‘s fork stanchion tubes were tapered into a thinner midsection, and new damping was added. The steel components on the Kayaba shock were replaced with lighter aluminum pieces. Oversized Pro Taper Contour bars replaced the old-school steel handlebars. Aluminum bolts replaced the previous steel bolts on many parts of the bike. The silencer’s perf-core section was shortened by 75mm to improve throttle response without increasing sound.

2008: The YZ125 in 2008  inherited the front-brake caliper, fork stanchions, lower fork bracket and a chain guide from the then-current YZ250F. Also, a new reed valve was added, and the front master cylinder piston was made 1.48mm smaller. 

2009: Yamaha upgraded the oversized, steel, serpentine brake-hose holder with a 32-gram-lighter aluminum clamp. The 2009 YZ125 also earned a new seat cover and a new Dunlop 742F front tire. 

2010: No changes beyond Bold New Graphics (BNG). 

2011: Yamaha stopped making different bikes for the American, European and Japanese markets. The switch to one model, with a worldwide global spec, was a money-saving strategy. The majority of changes were designed to make the 2011 YZ125 powerplant run on the lower-grade gasoline of third-world countries. For example, remember when Yamaha shortened the silencer’s perf-core by 75mm in 2007 to improve throttle response? Well, under the worldwide global spec, the silencer was lengthened by 75mm and the core enlarged from 27mm to 30mm. Additionally, the 410 main jet was exchanged for a 430, while the 6BFY42-3 needle was swapped out for a 6BFY43-3 needle. 

2012/2013/2014: Besides playing hop-scotch from a blue to a white to a blue rear fender, these three model years only saw BNG.

2015: The big news was that the 2015 YZ125 was upgraded to the “arrow” design plastic of the Yamaha four-strokes. It also got improved SSS fork damping and a new airbox. 

2016: A gold chain, black rims and BNG were added to the 2016 YZ125.

2017: The front rotor was increased from 250mm to 270mm, and the brake pad material was improved on the 2017 YZ125. 

2018/2019/2020: The black rims were dumped in favor of blue rims. And, as with every model change since 2006, it got bold new graphics (BNG).

Q: WHAT DOES THE 2020 YZ125 WEIGH?

A: Without fuel in the gas tank (but all other fluids), the 2020 YZ125 weighs 201 pounds, which is what they claim. For comparison, the 2020 KTM 125SX hits the scales at a very light 192.5 pounds. 

Q: HOW DOES THE YZ125 HANDLE?

A: MXA tested the bike on everything from SoCal hard-pack to deep sand. The biggest surprise was how well the YZ125 handled in the deep sand. In rollers big enough to swallow the YZ125, it actually floated over the bumps better than most 250cc four-strokes. Best of all, the lightweight bike was so stable that it was self-righting, even when it got sideways. Surprisingly, for a chassis that is not far from being legal in vintage racing, the YZ125 still handles like a contemporary machine. 

It is often said that “Slow bikes handle better than fast ones.” Unlike most old wives’ tales, this one is true. Fast bikes tend to wear a rider out, generate arm pump and go from stable to “Oh, no!” quickly. It is easier to make a mistake on a fast bike‚ or, more accurately, it is harder to make a mistake on a slow bike.

Q: WHAT DID WE HATE? 

A: The hate list:

(1) Engine. The Yamaha powerband gives up easy horsepower on top, which exposes its biggest weakness—lack of speed.  

(2) Front tire. We didn’t know any manufacturer was still spec’ing the less-than-stellar Dunlop MX52 front tire. A simple change to the current Dunlop MX3S or MX33 front tire improves the YZ125 at turn-in. We don’t mind running the rear MX52, as long as the conditions are on the hard side.

(3) Price. The $6599 price tag makes the YZ125 the lowest-priced, full-size premium motocross bike on the showroom floors, but all it buys is 2006 technology. Think how awesome, albeit expensive, the YZ125 would be today if Yamaha had invested money, research and development in it over the last 14 years.

Q: WHAT DID WE LIKE?

A: The like list:

(1) Clutch. We rarely 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 exceptional. Lucky for you, they come stock on the entire Yamaha line.

(3) Maintenance. Anyone who is slightly mechanically inclined can change a YZ125’s top-end. A Vertex piston kit costs $109.95 (www.vertexpistons.com). You can buy two YZ125 pistons for the price of one YZ250F four-stroke piston.

(4) Bulletproof. The YZ125’s reliability is legendary‚ because its 14-year-old parts have been time tested to eliminate failures.

(5) Weight. At 201 pounds, the Yamaha YZ125 is easy to ride and very agile. We loved dodging the bumps that our friends on four-strokes had to hit. 

Q: WHAT DO WE REALLY THINK?

A: If you’re riding for fun, there is no better bike made than the 2020 Yamaha YZ125. It is superb project-bike material, a great transitional bike for a rider moving up from mini-cycles and makes an affordable play bike; however, it’s hard to fork over $6599 for a bike that has changed so little over the last 14 years. We say that not because it isn’t a good bike; it’s just that you could buy a used YZ125 for a lot less money and still get the same performance.

Kayaba’s SSS forks are the best showroom forks made. On the YZ125 they are set-up for light riders.

MXA’S 2020 YAMAHA YZ125  SETUP SPECS

This is how we set up our 2020 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 2020 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 will have to go stiffer on the fork springs. Faster riders can dial in more compression and use the crossover effect of rebound damping to get the stock fork springs to work adequately.

KAYABA SSS SHOCK SETTINGS
For hardcore racing, we ran this setup on the 2020 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. It tracks straight and is in tune with the bike. We love this shock.

YAMAHA YZ125 JETTING
With 14 years to iron out the bugs, Yamaha has the jetting down pat. It ran clean right from the first kick. 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 in 2011. 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.