An Ultimate Guide to Yamaha YZ125: Speed, Specs and features

Yamaha possesses huge respect among motorcycle manufacturers around the world for their world-class models. They are synonymous with high-performance bikes. From race tracks to dirt trials, you will find their models dominating everywhere. Among those bikes, there is one model that might have grabbed your attention. And this is the Yamaha YZ125. Although a beginning model, it is an amazing bike when it comes to their dirt bike series. It is no less than a flying tech thanks to the two-stroke engine.

Moreover, this model keeps on surprising you when it handles all the bumps with ease. Its smooth fork, effective cooling system, and powerful engine ensure smoothness. If you are a bike lover and want to have an insight into this model, this article is like a god-sent. It consists multi-dimensional analysis and review of the Yamaha YZ125. Based on this, the pros and cons along with the decree form the later part of this article. So, fasten your seat belts, and begin.

Cursory Glance at the Yamaha YZ125

Yamaha launched the first model of YZ125 in 1974. There was no change to its frame till 2004. In the frame, visible was a single backbone made of steel. Since this brand uses steel, the previous models were heavier than the later ones. Roughly putting, the steel version weighed around 175 to 200 pounds.

In addition to this, the bike comes with a two-stroke engine. It does use reed valve induction whose displacement is 125cc. The earlier models from 1974 to 1980 were air-cooled. However, Yamaha began to use liquid cooling from 1981 onwards. When it comes to horsepower, it possesses 35 HP. Low horsepower, you may wonder. Don’t be deceived by it, as this model is a beast and has won several AMA National Motorcross Championships.Read the complete review of yz125 dirt bike.

Specs of Yamaha YZ125

A brief look at its specs is as follows:


Engine type 125cc liquid-cooled 2-stroke; reel-valve inducted 

Ignition CDI

Fuel delivery Mikuni TMX 38

Compression ratio 8.6~10.7:1

Bore and Stroke 54mm * 54.5 mm

Final drive Chain 

Transmission Constant-mesh 6-Speed; multiple wet clutch 


Seat height 38.4 in

L * W * H 84.1 *32.6 * 51.0 inches

Wet weight 207 Ib

Fuel capacity 2.1 gal

Ground clearance 14.4 in

Wheelbase 56.8 in

Trail 4.3 in

Rake 26.0


Suspension/front KYB speed-sensitive system inverted fork; fully adjustable, 11.8-in travel 

Suspension/rear KYB single shock; fully adjustable, 12.4-in travel 

Tires/front 80/100-21 Dunlop MX52

Tires/rear 100/90-19 Dunlop MX52

Brakes/front Hydraulic disc 270mm

Brakes/rear Hydraulic disc 245mm

Now let’s have a detailed review of these specifications and features.

1: Lighter Frame

The lighter is the frame of this bike. Unlike previous models, its frame is made of an aluminum alloy, not plastic. Furthermore, its design is race-ready. Therefore, the brand has used the YZ125 for multiple races. In addition to weight, aluminum gives the required amount of integrity. As a result, this semi-double cradle frame is not only flexible but also solid. Since trail ridings are usually quite rough, this frame is ideal for any adventure you want to have. It will not disappoint you.

2: Riders-centric Chassis Design

By just having a glimpse of its chassis, you realize that this bike was manufactured with riders in mind. Not only it is extremely user-friendly to avoid fatigue and exhaustion but also has an ergonomic design. What is more, so well-tuned is the chassis of this bike that handling and moving it seems effortless. Experienced riders will enjoy riding this bike. It really is fun to ride the YZ125. Last but not the least, it also gives you confidence for bigger leaps if you still are learning. In short, its design manifests the expertness of the manufacturers who knew what requires in having a comfortable ride.

3: Two-Stroke Engine

When it comes to the engine, it is 125cc. Being a two-stroke engine, it produces more torque in case of high rpm. In fact, more powerful this engine is than four-stroke engines. More than more, Yamaha also switched to liquid cooling in this mode in order to maintain the heat. The said cooling system does not let overheat this powerful engine, ensuring a much better acceleration. Hence, the performance is magnificent from any mid to high rpm level.

4: High-Performing Braking System

Brakes are extremely important in trail riding. If they don’t work, death possibly will. Due to this reason, an outstanding braking system is what safety and trail ridging depend on. As far as dimensions are concerned, the front brake of the YZ125 is a 270mm Hydraulic disc brake. While the rear brake is a 240 mm Hydraulic disc brake. With these responsive brakes, you can easily stop the bike at any speed fast.

Besides that, reducing unsprung weight on the light wheel is also greatly helpful for the functioning of these brakes. What that means is more speed. On top of that, feel also exists.

5: A New Exhaust System

Dissimilar to the earlier YZ125, the model is equipped with a different exhaust. This is because Yamaha taking a different path with the exhaust. It comes with a brand-new expansion chamber. Except that, the design of the exhaust muffler is different. Just like dieting and losing fat, it is also smaller now. Also, the system gives an attractive and slender look. It seems Yamaha perfected this model.

6: KYB Fork-Industry-Leading

What Yamaha did for the fork also deserves love and appreciation. The invented KYB Fork gives you outstanding performance along with being extremely comfortable. With a lead spring, this fork accompanies a speed-sensitive system. With this leaf spring comes the mid-speed valve. That is why it ensures more accurate damping.

In this fork, there is also 11.8 inches of travel which makes your ride very smooth. You will also notice how comfortable it is to jump as well.

Top Speed of the Yamaha YZ125

The maximum speed you can touch while riding this bike is 70 miles per hour. It is slightly over 112 km per hour in terms of kilometers. For a bike that comes with a 125 cc engine, having this speed is quite impressive. However, this speed differs depending on the model year. The weight of this model was increased or reduced several times in the past. These fluctuations in its weight significantly affected its top speed either in a negative or positive way.

If we talk about the new model of 2022, the top speed that you can reach is 70 miles per hour. With the two-stroke 125cc engine you can outcompete your competitors easily. The reed valve induction system of the YZ125 is responsible for this amazingly fast engine. This bike runs like a beast with an unbelievable bottom end and robust mid-range acceleration.

Want to Increase the Speed of YZ125?

No doubt, the Yamaha YZ125 is an astonishing piece of tech. it is exciting and fun to ride this bad boy. However, fun must be unlimited. You do have mods for having extra fun. Numerous different mods in the market can increase the speed of this bike further. Are they costly?

There are some suggestions in the latter section about how you can better your Yamaha demon. Do the following:

Use a 144cc engine kit

Upgrade gear to 13/49

Use an upgraded valve system

Given the above-mentioned specs and features, there are some pros and cons of this model. Based on these, you can make a decision whether you should purchase this bike. The positive and negatives points of the YZ125 are as follows:


Powerful engine

Gives an exciting riding experience

Superior handling

Adequate weight

Low cost for maintenance


Lacks bottom end

Not an option for beginners