YZ125: My New Favorite Bike

I just bought a brand new 2023 YZ125 so I could review it firsthand for you guys and give you all the information you’re looking for.

(I’m hoping to be able to buy more bikes to review and share with you all in the future.)

I can’t stand it when I buy or own a bike, like this YZ125, and I can’t find a specific answer to my question quickly. You either have to dig through a bunch of crappy sites or flip through the bike’s manual. Both suck.

Here at Dirt Bike Vault, I set out to solve that.

My goal is to not only answer any question you’re looking for about the YZ125, but to give you the answer quickly and make it simple to find.

I’m going to provide the most common and important information about the YZ125 at the beginning of this article. I’ll follow that up with my review of the bike and experience with it, detailed information about the bike and its specs, and wrap up the article with frequently asked questions.

You can click the topic you’re looking for in the table of contents below to go directly there, or simply scroll to the section you need below.

Most Important & Common Want-to-Know Information about the YZ125

YZ125 Horsepower

As dirt bike riders, we have to know how fast our bikes go and how much power they have. Race bikes and motocross bikes, like the YZ 125, make us want to know even more.

The YZ125 horsepower is 34.44 hp.

Check out how this horsepower translates into the YZ125 top speed.

Electric Start or Kick

It’s not super common to see electric start on 2-stroke bikes. It has been becoming more popular with KTM including it in some of their new 2-strokes, but Yamaha didn’t include electric start in the new YZ 125. The YZ125 still does not have electric start — it has to be kickstarted.

Below you can see no electric start button on the handlebars and a Kickstarter.

YZ125 Weight

Prior to buying this new 2023 YZ125, I was riding a 2021 YZ450F and a 2022 YZ250F. I had also owned a YZ250, but sold it about a year before getting this YZ125 last month, so it had been a while since I rode it.

One of the first things I noticed about the YZ125 was how light and narrow the bike felt.

My dad had asked me what the weight difference was between the bikes before I rode the YZ125 for the first time. I told him the difference was roughly 30 pounds, and he said it’d be a huge difference.

I thought he was wrong, when in fact, I was wrong.

It was absolutely noticeable. The YZ125 felt a lot lighter. I was surprised.

I should’ve known he knew what he was talking about, he’s been a professional mechanic with his own business for over 30 years…

So what is the YZ125 weight? The YZ125 weighs about 209 pounds according to Yamaha.

Carbureted or Fuel Injected

Similar to the electric start I mentioned earlier, it’s not common to see fuel injection on 2-strokes yet. KTM has started doing it, but not many (if any) other manufacturers have.

I was hoping that the new 2023 YZ125 would have it, but unfortunately, it does not. The YZ125 does not have fuel injection — it is still carbureted.

You can see the full carburetor setup on my YZ125 below.

YZ125 Seat Height

I didn’t do a lot of research on the YZ125 before I bought the bike, so I was a bit surprised to learn that the seat height was actually taller than the seat height of my YZ250F — by almost half an inch.

The YZ125 seat height is 38.6 inches.

The seat height on my YZ250F is only 38.2 inches. I know that doesn’t seem like a lot, and it’s not, but I expected it to be the other way.

When I put the two bikes side by side in my dirt bike trailer, the YZ125 was noticeably taller. This was partially due to the suspension on my 250F being worn down (about 30 hours on it) and the YZ125 suspension being brand new, but still. The YZ125 was taller by more than I expected.

Suspension

For those who may not know, Yamaha is known for having some of the best stock suspension out of any of the major manufacturers — if not the best. The YZ125 suspension is no different.

In the front, the YZ125 comes with KYB Speed-Sensitive System (SSS) fully-adjustable inverted forks with 11.8 inches of travel.

The rear shock is also KYB, it’s a fully-adjustable single shock with 12.4 inches of travel.

The KYB rear shock is good, but the KYB SSS forks that I mentioned above are real good.

Below you can see the stock KYB SSS forks on my 2023 YZ 125.

Here you can see the rear shock. It comes stock with the silver spring.

Removing Suspension

The 2023 motocross season is about to start for me. To get prepped, I had to take the forks and rear shock off my YZ125 to bring it to Factory Connection to get it set up for my weight.

Up until now, the suspension has just been stock. Factory Connection will revalve it and set it all up for my weight and ability.

I did this same process for my 2021 YZ250F at the same time I did it for my 2023 YZ125. The YZ250F and YZ125 forks came off the same. Super easy.

But, the rear shocks come off quite a bit different.

The YZ250F rear shock comes off easily. Take the seat off and loosen the tank, then you can easily unbolt the rear shock and lift it up through the frame where the seat and tank were.

For the YZ125, it was a bit more difficult and took more work. I had to take the subframe off and disconnect the air box from the carburetor. Without doing that, there isn’t enough room to get the rear shock out.

Gearing

The YZ125 comes stock with a 13-tooth front sprocket and a 49-tooth rear sprocket.

You can see the 49-tooth rear sprocket on my stock YZ125 below.

YZ125 Wheels and Tires

The Yamaha YZ125 comes stock with a 21-inch front wheel and a 19-inch rear wheel. The front tire dimensions are 80/100-21 and the rear tire dimensions are 100/90-19.

The bike comes stock with a Bridgestone Battlecross X20F tire in the front and a Bridgestone Battlecross X20 in the rear.

I was a little disappointed to see the bike came with Bridgestone tires. They’re fine — they work well and there’s nothing wrong with them, I just personally prefer Dunlop tires. At least it came with a soft terrain tire, which is my preference.

Since buying the YZ125, I’ve also bought a dirt bike paddle tire for the rear, specifically Dunlop’s MX12 (which has been replaced with the MX14 as of this writing).

My YZ125 Experience and Overview

Starting with just the visual appearance of the bike. I love it. I like it more than I do the older styles. It’s not a ton different, but just enough. The 2021 and earlier models weren’t bad, I just like this one better.

I previously owned a 2017 YZ250 that had pre-2022-style plastics. Again, not bad, I just like the post-2022-style plastics better.

Yamaha officially released this plastics kit/style with the release of the 2022 YZ125 and they kept it for the 2023 mode as well. Below is a picture of my brand new 2023 YZ125 before it had any time in the dirt.

The first time I rode the bike, it did feel a bit slow. This isn’t really the fault of the bike itself. It felt slow because I had just spent the last 3 or so months mainly riding a YZ450F. Of course, a YZ125 is going to be noticeably slower than that.

That said, I actually had a lot more fun on the YZ125 than I did on my YZ450F. A lot of people like the 450s because they can be “lazy” while riding them and still go fast.

You can’t do that on a 125. You have to really ride a 125 hard to make it go fast.

That doesn’t bother me. I personally have more fun on the 125.

Admittedly, I was a bit nervous to buy the 125 because I did not like my YZ250. The YZ250 I had was the first dirt bike I ever bought and I didn’t like it. I thought it was because it was a 2-stroke, so I sold it to buy two 4-strokes — a YZ250F and a YZ450F.

I loved both of those bikes, so I assumed it was just that I didn’t like 2-strokes.

I decided to give a 2-stroke a try again when I bought this YZ125. Thankfully I did because I love it.

As I mentioned earlier in the article, the YZ125 is noticeably lighter and narrower than my YZ250F and YZ450F. I like both of those aspects of the bike.

The handlebars also feel a bit taller on the YZ125. If you look at the neck of the frame below the handlebars, there seems to be a lot more of an upsweep shape than on the 250F.

After riding my YZ125 for 5-6 hours, then hopping on my YZ250F, the handlebars on the 250F felt quite low.

Overall, I am really happy with this YZ125 and am glad I bought it.

But, there are a few things I want to say that aren’t so great. Some are the bike’s fault, others aren’t, but I wanted to at least share them.

Check The Fuel

The first thing is to always check the gas in the bike when you buy a 2-stroke, like the YZ125. Even if you buy it from a dealer. You’d like it’s safe to assume that a dealer would put the right gas in it, but you never know.

I drained the tank when I got it home from the dealership before I even started it for the first time. I wanted to make sure they actually did pre-mix it and that they used the right ratio.

I run 32:1 pre-mix in my YZ125 with Amsoil and VP110.

Who knows, the guy assembling the bike could’ve built 50 4-strokes before your 2-stroke and forgot that the fuel needs to be pre-mixed. I’d rather take the 20 minutes to double-check so I don’t blow the bike up right away.

A bonus tip here: be sure to check your spokes after your first ride or two. This isn’t really the fault of the assembler, but spokes often come loose when they’re brand new.

Hard To Start

I did 4-5 hot-cold cycles on the bike, then rode it around for about 15-20 minutes 2-3 times to break in the engine when I first got the bike. A few days after I did that, I took the bike to a local motocross track.

When I got to the track and rolled the bike out of the trailer to start it, I could not get the bike to start. I kicked it and kicked it and kicked it. Would not start.

After kicking it over and over again, I eventually got it to start and it ran fine the rest of the day. Started the first kick with no problem all day after that.

Then, it happened again about a week later when I went to start it for the first time that day. This time it started a bit easier than before, but still took a bit.

It really wasn’t a big deal, and not a real issue with the bike. Just a bit of a nuisance.

Since then, it’s started easily every time.

Throttle Wide Open

On my second or third track day with the bike, my YZ125 kept idling really high, almost as if the throttle was stuck wide open — but it wasn’t. This wasn’t a case where the throttle was getting stuck.

Rather, I’d be off the throttle and the bike would start revving to the moon.

Checked the throttle cable, throttle adjustments, made sure the throttle cable was in the top of the carburetor securely, and adjusted the idle down a bit. Nothing worked.

I parked the bike for the rest of the day because I couldn’t get the issue figured out and just rode my YZ250F.

I brought my 2023 YZ125 to my dad later that night, who has been a professional mechanic for over 30 years, and of course, I couldn’t get the bike to act the same way.

He’s not able to fix a problem he can’t see or hear.

We chalked it up to possibly some dirt being stuck in the bowl of the carburetor and it swishing around while riding, causing an issue.

Since then, it’s been fine with no issues.

Issue with Transmission

This here is my biggest concern with my YZ125 so far.

As I mentioned, I bought it brand new from a dealership and it’s a 2023 model.

The first few days of breaking in the bike, it was very, very hard to get the bike to go into neutral. Whether I was riding it or off the bike, it was very difficult to get into neutral.

The old rocking-the-bike trick didn’t help either.

After the bike broke in a bit more and I rode it, this problem seemed to go away. It got easier to shift into neutral.

Then, I started to notice that sometimes the bike wouldn’t shift while I was riding it. I’d be doing laps at my local motocross track, going down a straight away, or coming out of a corner looking for another gear and the bike just wouldn’t shift.

This didn’t happen every lap, but it did happen frequently enough that it worries me. The reason it really caught my attention was that I was flying at a double that’s about 50 feet long when I needed to shift to make it and the bike wouldn’t shift.

It just got stuck in the gear it was in and revved to the moon. Thankfully, I made the jump, but this happened multiple times throughout the days of riding it.

I had a major transmission issue with one of my YZ250Fs at only about 45 hours, so I’m a bit worried about transmission issues. This YZ125 is brand new with less than 5 hours on it, so it shouldn’t be having any transmission issues.

We’ll see if it needs a new one soon. I’ll report back here if it does.

Update: November 19, 2022 — Transmission Issue

After looking into the transmission and shifting issue a bit more, it seems the 2022 YZ125 was recalled for the exact same issue.

I did a bit of research into which VIN numbers were included in the recall and mine missed it by a few hundred. This wasn’t surprising given that my bike is a 2023 and the recall only covered 2022.

But, this did have me concerned. I noticed my bike’s 30-day warranty only had a few days left on it, so I brought it to my local Yamaha dealership to get it checked out.

After having it for a day, they called me and said two different techs rode it in the parking lot, shifted through the gears, and they couldn’t replicate the issue. Without being able to replicate the issue, they were hesitant to open the motor and transmission because the cost of that labor would be on me if there wasn’t anything wrong inside.

Yamaha would only cover the costs under warranty if there was indeed something wrong.

I opted to not have them open the motor/transmission and I’d just pick up the pick. My dad has been building dirt bike and ATV race engines for over 30 years, so if something does end up being wrong, he and I can just fix it ourselves. No need to risk it with the Yamaha dealership.

I rode for a few hours at a local track today, the day after picking it up from the dealership, and everything seemed fine. I will report back here later as I put more hours on the bike. It may be a bit before I do because we’re entering the winter season here where I live.

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YZ125 Specs

Engine Specs

• Displacement: 125cc
• Bore x Stroke: 54.0 mm x 54.5 mm (2.13 in x 2.15 in
• Compression Ratio: 8.2—10.1:1
• Induction: Reed valve
• Transmission: Constant-mesh 6-speed, multi-plate wet clain
• Drive: Chain
• Engine Type: 2-stroke
• Cooling System: Liquid-cooled
• Number of Cylinders: Single cylinder
• Main Jet: #160
• Main Air Jet: #200
• Jet Needle: NYDF-2
• Needle Jet: 2.9 (#6)
• Pilot Jet: #75
• Transmission Oil Capacity: 0.74 US quarts
• Transmission Oil Capacity (Disassembled): 0.80 US quarts

Chasis Specs

• Front Suspension: KYB Speed-Sensitive System inverted fully-adjustable forks (11.8 inches of travel)
• Rear Suspension: Single KYB shock, fully adjustable (12.4 inches of travel)
• Front Brakes: Hydraulic disc 270mm
• Rear Brakes: Hydraulic disc 240mm
• Front Tire: Bridgestone Battlecross X20F 80/100-21
• Rear Tire: Bridgestone Battlecross X20 100/90-19

Dimensions

• Length: 84.1 inches
• Width: 32.5 inches
• Height: 51.0 inches
• Seat height: 38.6 inches
• Wheelbase: 56.9 inches
• Rake (Caster): 26.0 degrees
• Trail: 4.3 inches
• Ground clearance: 14.37 inches
• Fuel capacity: 1.8 gallons
• Weight: 209 pounds wet

Frequently Asked Questions About the YZ125