Yamaha YZ125 Review – Is It The Best 125 Two-Stroke Ever?

Since there’s not much hope in the economy coming back in the near future, dirt bikers are resorting to things that will give them the best bang for their buck. As a result, 125cc two-strokes have been rising in the used market. Why? Well, it’s pretty simple, actually. First of all, you can rebuild the top-end for $150 or less, which can be done in your garage with a little mechanical motivation and patience. They are great dirt bikes to start out on for motocross, as they teach you how to control the throttle, clutch, and controls. Probably the best part about a 125 2-smoker is that they’re an absolute blast to ride! They’re light, quick, snappy, and besides, who doesn’t like the smell of race gas and pre-mix in the morning?!

Which Decade?

Yamaha hasn’t changed their 2-strokes for a while. However, this doesn’t mean it’s outdated. In fact, that’s quite the opposite, as Yamaha has been building quality 2-stroke motocross bikes for years. As long as they make them, riders continue buy them. They are often the first dirt bikes to sell in a dealer, but let’s take a look at why these bikes are so popular in the first place.

1990’s YZ two-strokes are fairly similar. In ’96 they made some changes that lasted until the end of 2001. These are still considered some of the best motocross bikes, especially the 1999 model. They are fast, reliable, and are just a great overall bike.

In 2002 the frame changed, making it lighter, narrower, and more flick-able. However, many people didn’t approve because it switched to a 5-speed transmission. 125’s have a narrow power-band as it is, and some riders just like having that extra gear.

2005 and 2006 are biggest years for the Yamaha YZ125. In ’05 they changed to an all aluminum frame, made some engine changes, as well as changing back to a 6-speed transmission.

2006 Yamaha YZ125
2006 Yamaha YZ125

Power

Power has never really been an issue when it comes to the YZ125. In amateur ranks, these small-bore two-strokes can hold their own against 450’s with the right rider. Of course it can be harder to ride them faster, but they have the ability, and it’s extremely fun doing it. Although 125’s are known to have little to no bottom-end power, the YZ125 has always seemed to have a little more torque down low than the others in its class, making it manageable if you need to lug it in tight areas. Once you get to the mid-range you can start to feel the inner-beast come alive, especially on the later models. As soon as you hit the power-band on one of these tiddlers, you’ll know why they are so addicting. It may scare you at first if you’ve never ridden a two-stroke motocross bike, but you’ll be begging to do it again and again until there’s no more premix in the tank… Throw a pipe on this thing and get it properly ported, and you have race-ready engine on your hands (not that it isn’t with a stock engine).

In 2005, the YZ125 got a new engine and carburetor, which greatly improved the bike. It’s so crisp and fast that you don’t need to touch the bike to be competitive. Although, as the saying goes, it’s easier to make a fast bike faster… Slap a pipe on there, get it ported, run some race-gas, re-jet, and she’s ready to haul the mail!

Handling

While it’s light, fast, and flick-able, some people don’t like the way YZ125’s handle as much as other late-model 125’s. The CR125 has been at the top of its class in the handling department since the 3rd generation chassis came out in 2002. That bike handles extremely well with comfort. The 2002 and newer YZ125 are not far behind though, so don’t let that be the determining factor.

2005 was the first year of the aluminum frame, which is still claimed to be one of, if not the best 125 two-stroke made. It’s lighter, faster, handles better, and just overall rides more like a modern motocross bike.

Suspension

Yamaha continues to provide top-notch suspension in their motocross bikes, and the YZ125 is no different. The older bikes from the 90s left something to be desired compared to modern mx bikes, but in the 2000’s they have some of the best suspension out of the box. Bottoming-resistance is one of the leading factors of it being at the top of its class. The ride isn’t as harsh as some of the other bikes, but like any other motocross bike, you will want to get it re-valved if you weight less than 140lbs or more more than 170lbs depending on what kind of riding you do.

In 2006, which was the last year of any major updates, the YZ125 received new SSS forks, which are considered a big upgrade. If you can find a good deal on clean ’06, buy it! If you find a nice ’05, I would definitely buy that too. For someone that’s not a pro rider, you probably won’t notice much of a difference between the two. Besides, most racers get their suspension re-valved for their weight and riding style anyway.

You Should Get A YZ125 If You:

  1. Want a light, nimble, quick bike
  2. Like mixing gas and the smell of premix
  3. Want to go back and learn the basics
  4. Like snappy power
  5. Want a dirt bike that’s cheap to maintain
  6. Want to rub it in when you beat friends on four-strokes
  7. Don’t want to make the jump all the way to a 250F
  8. Want to rebuild top-ends at home

You Shouldn’t Get A YZ125 If You:

  1. Don’t like mixing gas or the smell of premix
  2. Want a smooth and very predictable power-curve
  3. Like checking valve clearances
2001 Yamaha YZ125 2-Stroke
2001 Yamaha YZ125 2-Stroke

I’ve owned my share of YZ125’s, and they’ve all been great. The most reliable motocross bikes I’ve owned, and they’re just so much fun to ride. Of course, the newer the better, but even a 1999 YZ125 is a great bike to get started in this awesome sport. Check out my other articles on how to find deals on used dirt bikes!

-Tom Stark

 

I Rebuilt My YZ125 In A Closet!?

It was more like a hallway, but the work area was still smaller than I wanted. I picked up a 2003 Yamaha YZ125 that had some major frame damage. The bike ran well but was not ride-able. The two options were to scrap the main and sub-frame, or take the time to bend and weld them back to their somewhat original form. Either way I would have to strip the entire bike down to the very last bolt and tie-strap. Just by looking at it I could tell this was going to be a difficult, yet exciting project.

I got to work tearing down everything on the YZ125, starting with taking the engine out of the frame. There were a lot of nuts and bolts from the plastics, engine, radiators, frame, and other miscellaneous parts that I had to organize into little zip-lock bags so I wouldn’t lose track of where they went when I put them back on the bike. In the middle of this process I got the sub-frame bent back and welded so that it would fit like normal. Being me, I decided to go the more challenging route of getting the main frame welded instead of paying a couple hundred for another one. Once I took everything off of the main frame my dad helped me by welding it.

I wanted to make this bike look good when it was finished, so I sanded and cleaned off the main frame to get it ready for painting. It took a while, but I managed to find some paint that was close to stock color shade. I then painted it with a few coats to make sure that it wouldn’t peel or chip right away.

Tear Down Process
Tear Down Process

The rebuilding process began just after the paint on the frame dried. This is the part where I had to move everything inside…. I started with the foot-pegs, front-end, rear shock, and swing-arm. Those went on pretty easily, so I then took the whole engine and bolted it up to the frame. The rear-wheel and handlebars with controls were next to go on. After that it was just the electronics, carburetor, plastics/tanks, seat, and a few miscellaneous things, such as the exhaust system.

Rebuild Process - Frame painted, front-end, rear shock, and swing-arm on
Rebuild Process - Frame painted, front-end, rear shock, and swing-arm on
Rebuild Process - Engine in, rear-wheel, handlebars on
Rebuild Process - Engine in, rear-wheel, handlebars, and controls starting to go on

After working inside for some time, this project was well worth the outcome. In the end I think the bike looks good, and I learned quite a bit more about rebuilding these modern dirt bikes (Check out my other article, “How I Built A YZ250F With A Box of Scraps” if you liked this one). Let me know what you think, and if you want to see more projects like this just give me a shout. Thanks!

-Tom Stark

Finished '03 YZ125 Project
Finished '03 YZ125 Project

Top 5 Motocross Bikes of the Decade


This past decade saw much change and technological advances compared to the 1990’s. The Pro National scene went from 99.9% of the bikes being two-stroke (Yamaha’s YZ400 was about the only thumper out there in the late 90’s). 2001 was the beginning of the end for the 125 2-stroke because of the YZ250F, and soon after, the other companies followed suite. By 2006 the scenario had done a complete 180. Within the past 10 years, there have been some atrociously made bikes, as well as the best bikes ever made. This list may not include the entire globe, but should cover the United States, along with many other countries that have similar inventory of bikes. My list is objective and unbiased; I am going by which bikes are being sought after and bought the most, both new and used.

5. Yamaha YZ250

Yamaha YZ250 2-Stroke

Yamaha is the only Japanese manufacturer that still imports their two-stroke motocross bikes to the U.S.. They have had it together the entire time, but the YZ250’s best years are 2005 and newer. The lightweight aluminum frame and updated suspension (2006) makes the bike nimble, quick, and easier to ride. Power right out the box is excellent for almost any amateur, so there really isn’t much you need to do for it to be competitive, other than a suspension re-valve for your weight and riding style. The YZ250 has quite a bit of bottom-end power for a 2-stroke, and has plenty up top. You can move the power-band around with an aftermarket pipe if you don’t like the stock curve. Probably the best modification for engine performance is porting. It’s relatively cheap, and if you get it done by the right person this bike will absolutely rip.

4: Yamaha YZ125

Yamaha YZ125 2-Stroke

I know I said that four-strokes have dominated the pro motocross and supercross scene the past several years, but that doesn’t mean people don’t buy two-strokes anymore. In fact, riders are realizing how expensive four-stroke motocross bikes can be if there is a major failure, so they’re moving back (or to) two-strokes. Don’t fool yourself, the 125 two-stroke is a very fast bike, even stock, when properly tuned. When James Stewart entered the pro-scene on a 125, his lap-times were often as fast or faster than a lot of the 250cc riders because he knew how to ride his KX125 so well. He continued to beat four-strokes in 2004 when 250F’s started becoming “the bike” to race, so you know the bikes wasn’t lacking, that much.

The Yamaha YZ125 has reigned has “the bike” to get in the 125cc-class for many years now. It may not have the best of everything, but as an overall package it’s arguably one of the best motocross bikes ever because it is versatile. Although, the motor hasn’t changed much since 2001, and the chassis/suspension since 2006, there really isn’t a whole you need to do to this bike to race it.

Unlike most other 125’s, the YZ125 has some bottom-end power. So if you’re not afraid to finger the clutch a little, you can turn it into a woods weapon because it is so light. The center of gravity is lower than four-strokes, adding to its maneuverability. I like riding both two- and four-stroke dirt bikes, but getting on the pipe and ripping it up on a YZ125 is just too much fun!

This bike also makes my top 5 list because of how easy maintenance is, as well how cheap it is to repair if something major happens because of less moving parts. A four-stroke engine costs 3-4 times as much if something catastrophic happens, especially if you have a shop do the work. On a two-stroke, as long as you change the oil regularly, a top-end kit (usually just a piston, rings, gaskets, etc.) costs around $100-150. Even if your cylinder gets scored you can re-plate it to new condition for about $200.

3. Yamaha YZ450F

You guessed it, another Yamaha. Not only are its two-strokes good, but so are the four-strokes. The first year of the YZ450F was 2003 (superseding the YZ426F). This is when the bike was titled “Impossible To Ride.” It did have a lot of torque just because it’s a 450, but the top-end power was unbelievable. It was hard to hang on to the bars for less-experienced riders (Here I’m thinking, “supermoto, supermoto….”). Well, it is a little harder to ride than most others in its class, but any 450cc motocross bike is going to have a lot of power if it’s fresh. Don’t let all the “internet hype” get to you, it was still a great bike. In fact, some say it had the best 450cc from 2003-2005.

2003 Yamaha YZ450F

The second generation YZ450F got even better (for the most part) in 2006 with the all-new aluminum frame. This reduced weight and helped with handling (more on that in a little bit). The power curve was changed considerably, changing from a top-end monster to a more mellow beast. Some complained, others loved it. Don’t worry, the engine is probably the easiest to change, it just takes a little dough.

Moving on to other things, the YZ450F’s suspension is good in stock form. Just make sure it has the correct spring rates for your weight and riding style. The handing on this bike is said to be an issue. Supposedly the steel frame was to blame and made it feel heavy and turn slower. I mentioned that 2006 is when Yamaha switched to aluminum frames for its four-stroke motocross bikes, and doing this resulted in better turning and handling for this bike. 2010 is really when handling was a positive for the YZ450F with the new bilateral-beam frame and centralized weight. It made it feel more like a two-stroke, but not quite because of its weight.

2. Honda CRF450R

Honda CRF450R 4-Stroke

Red has always been a popular color, and there’s a reason why; they make high-performance bikes. Honda’s CRF-R line is near the top in almost every performance category, but the thing that has held them back from others is the reliability. Granted these are full-on race-bikes we’re talking about, but some of Honda’s early model four-stroke motocross bikes have had some problems causing failure much sooner than others in its class. The valve-train malfunctions were primarily on the CRF250R its first few years, which is why I chose the CRF450R to be on this list.

The first year of Honda’s 450cc four-stroke motocross bike was 2002, when Yamaha was still making the YZ426F, so it had a little edge. The CRF450R helped bring down the two-stroke legacy in pro racing. You know something is wrong when Kevin Windham on Honda’s 450R is passing Ricky Carmichael (aka the GOAT) on an RM250 two-stroke. No disrespect to Windham because he is one of the smoothest riders in the history of motocross. It’s just that “RC” is clearly a faster rider when he is healthy.

Honda has been known to make dirt bikes that handle well. The bilateral-beam aluminum frame on the CRF450R is just the same as far as four-strokes go. Point it and it goes there. The ergonomics are great for most riders as well. Suspension has always been on par or better than other bikes in its class. Over the past few years Honda has been making their 450 easier to ride for more riders right out of the box, bringing out the fuel-injection (second company to do that behind Suzuki’s RMZ450). There have been some glitches, but then again, what bike doesn’t when it introduces something completely new?  Overall this is a very powerful, easy to ride fast, and great handling bike for riders of all experiences, which is why it’s so popular.

1. Yamaha YZ250F

Yamaha YZ250F 4-Stroke

Yep, that’s right. The YZ250F is The Top Motocross Bike of The Decade. Surprised? You shouldn’t be. It’s the most popular 250cc four-stroke motocross bike, and for many good reasons. It was the first one made, and by a few years two. The first year of Yamaha’s 250F was 2001, and it was an instant success. People saw how powerful it was and how much torque it had compared to a 125 two-stroke.

Yamaha knows how to make a four-stroke motocross bike, plain and simple. Their 250F has always been known as the most reliable out of its entire class, even in its early years. It was a bit porky and hard to start at times in ’01 and ’02 with its manual decompression, but once they figured that out in 2003 this bike was a force to be reckoned with. No more clutching out of every corner, bogging out and casing jumps, or having to perfect your shift points. Once the pros started riding them, everyone wanted one. The thumping and thundering sound of a four-stroke ripping up the track is loved by many, but hated by many as well.

The YZ250F’s engine characteristics weren’t number one once all the other companies figured their 250F’s out, but it was mainly lacking some down-low. It was a pretty easy fix with an aftermarket exhaust or cams, but that’s only if you wanted it easier to ride with a smoother power-band. Yamaha has always had great suspension, and the YZ250F is no different. Ready to race out of the crate as long as the spring rates fit your weight and riding style.  Ergonomics have been a positive for the most part. The early models were a little chunky, so the newer you get the better.

Handling is something that people always complained about, but I think that most of the propaganda came from people reading magazine reviews. Statements like “It can’t turn right,” or “It stands you up in corners” are usually from people that have never ridden the bike. It’s not as dramatic unless you are a Pro or fast A rider. You can also re-valve the suspension, change bars, triple clamps, springs, ride height, and many more things to get it to corner. Other than that, the YZ250F is a great bike and is very reliable. There are riders that get 200+ hours on stock and with everything still in-spec if they aren’t racing it hard. That’s saying something for a high-performance, high-revving machine.

Now remember, this list is the top motocross dirt bike of this past “Decade”. If it was within the last few years this list would more than likely be completely different. These bikes have been the most popular for the most amount of time in the past ten years. The reason why I did that instead of the last few years is because not everyone has the budget to buy that new of a bike. Some riders that are looking to start out in this extreme sport want cheaper, yet competitive and reliable bikes. I want to give those riders (YOU) the benefit of knowing these things so that you can stay with the competition.

-Tom Stark