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Written By: Gardner Tarlow
The last time I rode a Yamaha YZ125 was the all-new version in 2022. At that time, I had been riding a 2021 Husqvarna TC125 and 2022 KTM 125SX. When the new YZ125 came out it was a completely new motor on a tried-and-true frame and suspension package. I thought for sure it was going to be my new favorite 125. Unfortunately for myself, I only got to ride the bike for a few hours and as much as I liked the motor, I couldn’t get the suspension 100% dialed in for myself and so I handed off the bike feeling a bit unsatisfied. How does that happen with 125? I will never know!
In 2023, I was able to test the all new KTM 125SX TBI bike (see article Keeferinctesting.com) and although I really liked that bike, I still wasn’t crazy about the air forks as well as the motor required a bit of coaxing in “stock” form whenever you made an error in your corners. The other concerning issue was that I had absolutely NO working knowledge about how the TBI system worked or any confidence in my ability to work on the bike myself.
Come 2024, Kris has given me another opportunity to test the YZ125 but this time for a prolonged period of time. I got the 50th anniversary 2024 YZ125 and dam if it isn’t sexy. White may be a pain to keep clean but it sure looks good when it is clean. The 2024 YZ125 hasn’t changed from 2022 with the exceptions of bold new graphics and possible minor suspension tweaks. The bLU cRU version is listed for $7,099 and the 50th anniversary version for $7,299.
The YZ initially got its major over hall in 2005 with the aluminum frame and in 2006 with KYB SSS suspension upgrade. Between 2006 and 2021 their where minor changes here and there in attempts to keep the bike progressing. The motor had always been a good off the bottom 125 compared to its competition and that along with its excellent handling manners is what always kept the bike relevant. In 2022 the motor got a complete redo to provide a more mid and top end performance motor. The bottom end still maintained good power but it was a little less error friendly than the previous generation motor. The hope was to align the new motor to better compete with the competition. The chassis and suspension have always been the YZ125 sweet spot and the 2024 generation bike continues to hold down that position. Any day railing around the track on a YZ125 is a blast and will bring a huge smile to anyone who swings a leg over the bike.
I’m a senior vet rider, probably open novice, 5’10”, 185lb on a good day. I’m a 60/40 track and hills rider. Bikes of choice are normally two strokes or a 250F. I typically ride Glen Helen and Cahuilla for local tracks and if I’m on a 125, I typically keep it on the vet tracks for the most part. I am not the classic 125 demographics, neither age nor size, but more and more vet moto guys are enjoying the close racing found on small bore bikes that don’t penalize you with every mistake.
The suspension on the YZ125 is ideally set for 150-175 lbs. but despite my size the suspension is still capable on the track. The SSS forks and KYB shock are very predictable and manage big hits without any harsh transition to the rider. The SSS forks are consistent with performance throughout the day and provide a front end that feels planted on both flat and off camber turns. I tend to run my suspension fairly soft but for those riders above 175 lbs, stiffer springs will be required. The rear shock is also under sprung for myself but still performed well on big hits, heavy braking bumps and acceleration bumps in the ruts. Optimal sag for the YZ125 is 100-102mm but due to this rider size, I ran sag at 105mm as I wanted to keep the free sag in an acceptable range without too much preload.
The handling of the YZ125 chassis has been a class leader for years and the 2024 YZ125 remains second to none. The chassis has a supple feeling without any harshness or sense of deflecting. The chassis and suspension felt planted and comfortable on lean angle and set up into corners, the bike wants to stay in the rut mid corner and exits and finishes corners very well. The rear end even though under sprung for this rider, didn’t seem to squat and disrupt mid corner and exit corner performance to any appreciable extent. I did notice some slight repeated head shake with fast, heavy braking bumps which I assumed was due to the fork being under sprung and low in the stroke of the fork. Outside of that, the handling, performance and fun factor of this bike is unreal.
The motor on the YZ125 was all new in 2022 and remains the same for 2024. The motor has a solid bottom end with strong mid-range and top end performance. Is this motor better than the previous 2021 motor? Depends on who is riding it. For the faster more experienced rider, the new motor will produce faster lap times. The 2021 YZ125 motor was more bottom end oriented with a good transition to mid power band but didn’t have the top end needed to be a class leader in horse power performance. In a class all about horse power the pre 2022 Yamahas hung tough with their handling prowess but struggled against the Austrian 125s when it came to all out-motor performance in stock form.
In stock form the 2024 YZ125 is a solid handling and performing bike. I was provided the bike to test after Kris had done some jetting modifications to the carburetor (raised needle to 2nd position). I must say the bike was pretty spot on with jetting when I got it. Despite the spot on jetting my less than optimal 125 physique (185 pounds) exposed some potential low-end issues with the bike’s performance. Specifically, in sandy sweepers, deeper soil corners and bigger hills coming out of slow corners, I really needed to abuse the clutch to the keep the motor pulling in the mid-upper range of RPM’s with any rider error. The Yamaha clutch by the end of testing was still performing well and required very little adjustment.
By the 10 hour testing mark I decided it was time to try some easy bolt on modifications. Easiest and least expensive modification was to add an additional tooth to the rear sprocket to assist the YZ125 in those situations noted above. The Stock motor with the new Renthal 13/50 sprocket (stock 13/49) was a definite improvement in bike performance. The ability to not have to abuse the clutch and in general pull harder in deeper soil and bigger hills was immediately felt. I was now able to use third gear more in corners and the bike responded more effectively to clutch slipping. For riders north of optimal 125 weight this is an inexpensive improvement with nice performance gain.
The next modification was the Pro Circuit Works pipe and R-304 shorty silencer. The pipe mounted without any issues and looked awesome. From the first fire of the motor the bike had a distinctively different sound that was crisp and unmistakably like a modified 125. I initially ran this pipe with the stock 13/49 gearing. On the track the pipe provided improved power throughout the entire power curve. The bottom end was more forgiving (easier to recover when I made a mistake) with a better snap to the throttle and significantly reduced the effects of rider error. The ability to work the clutch and get the motor back to optimal RPM was improved by the PC performance. The mid and top end pulled stronger as well as the ability for over-rev was improved. The PC system absolutely improved the performance of the bike.
With the PC system on the bike, I put the one tooth larger Renthal 13/50 sprocket back on the YZ125 and the combination of the two items proved to work very well together. The YZ125 now was able to easily pull taller gears through deeper soil as well as pulling those gears better up Glen Helens main hill. The combination of the PC pipe, 50 tooth rear sprocket and good jetting made this YZ125 very quick corner to corner. My only complaint with the YZ125 was the Bridgestone Battlecross X20 front tire. When the tire was new it performed well but as the tire wore down (6-8 hours), I noticed an increased frequency of the front tire braking loose on off camber fast corners. My preference would be a Dunlop MX3S or MX34 which in my opinion seems more predictable as the tire wears with increasing hours.
The Yamaha may not be the most advanced 125 bike on the track but it is without a doubt a race worthy bike that in its simplicity makes it very easy to work on by any garage mechanic. The Yamaha is a tried-and-true race bike that has a decade worth of race proven modifications, both bolt on, or fully modified that can make this 125 a class winner for any rider.
Viva La Two stroke.
