Which 125 would you get?

I picked up a 26 YZ, it’s a great bike. At 64 I was looking at just having FUN!🤪

I have raced, and built my fair amount of 125's and also had a sx150. For me it would be a simple choice to go with the 150 as a play bike for the broader power. in stock form you get what a expensive tuned 125 would be.

I hate ktm with all of my heart but it's hard to argue against the 150.

My 2013 150SX is still my all-time favorite bike. I don't think I'll ever sell it

Id get a TM over all those 

You can't go wrong with either condition will be the most important thing. 

Now I owned from new a 2006 yz125 that I modded into a yz144. Loved that bike had it for 15 years. 

Now I own a 21 150sx I bought new. 

I'm 190 - 200 max fully geared up. My yz's suspension was stock the entire time I owned it. Pretty much was a set it forget it setup. 

Power wise stock yz as a 125 it would get pulled by the 150sx. Vs my yz 144 they were much closer. But my yz needed a high compression head setup where I had to run trick 110. Which would wear out the ring faster on the exhaust bridge = more frequent top ends. A similar setup on pump gas on the yz wouldn't have been as powerful. 

Depending on how hard you're with the clutch the yz will need an upgrade. 

The ktm makes as much power actually a little bit more. Then my modded race gas yz setup. But the ktm does it on 92 pump gas. Has a dual ring piston that last longer. Comes with a billet steel clutch basket stock. 

Ktm negatives for me where the air fork it's not bad stock. But I could never get past the lack of feel. It had right after corner entry to mid corner. And the funky feeling it had on slapper landings. Doing the kyb swap for me made a big difference in feel especially cornering traction. 

Other ktm suspension negative for me was the stock rear spring was too light. It would squat too much. And blow through the last half of travel. I put a stiffer spring on it a 4.8 and it helped rear end hold up and cornering improved and stopped the excess bottoming out. 

06 21 yz125 better jetted right away my 21 150sx way too rich. I ended up doing the pwk swap. 

X2

2010-15 150SX if you can find them.

If not, any 96+ YZ

I'm 37, 6'2", & 200 lbs with gear. I have a 2025 KTM150 and the thing is an absolute blast. I put a heavier spring in the rear and had it re-valved. If I were to do it again, I'd just put on a heavier spring. I'm not racing so I don't care about speed off the gate etc. The only place I've been wanting for power is if there is a decent jump right out of a corner. Honestly, I think the issues is more on me than it is the bike. Otherwise the bike delivers smooth power, handles like a dream, and again is a blast to ride. Get a 150 if you can. 

I'm not sure now, but when the '22 YZ came out, it seemed like they had a bit more top but didn't run as crisp down low as the '05-21. I have a '19 with exhaust, vforce and JD jet kit and it runs amazing. I changed the seat to flatten out the foam a bit, to help the ergos. I think if you want instant power, a very well-rounded chassis, very good suspension but don't mind needing to shift, then you can't go wrong w the '21 YZ. A buddy of mine has a '19 150Sx and it is done up with similar mods, was just all rebuilt. Beautiful bike but I honestly don't really like it much. The power has a short window, the chassis feels long or less easy to flick around and the suspension I do not like on that bike. He loves it. But every time I ride it, I just come away sort of 50/50 on it. I personally feel like the YZ is fun on every track and the power is always just so crisp. If you can shift as the bike needs it, you'll feel like you can't lose. It just stays singing and the chassis to me is the perfect balance.  The KTM is unbelievably fast for what it is, but to me it has tracks that suit it and others that don't. That is my back to back experience, since I swap with that bike quite often. Both bikes are well maintained etc. But obviously the KTMs are monster motors and can be tweaked into great bikes too. I've had a few YZs of that '05-21 gen over the years and I think it's just a bike that you can't go wrong with.

I generally trust Yamaha’s over KTM’s any day. 

If you still race & want extra power maybe the 150 is your bike - otherwise the YZ is an all around, time tested FUN bike. 

Another point to consider - handling. Have you ridden many KTM’s? Their feel is unique compared to Japanese bikes. Some love it, some hate it. 

I wonder if this is the case with the 125's? I'm curious. Its Certainly true with the 4 strokes.

I have the same bike - bought new in 2013.  It is still my only motocross track bike.  I am almost 70, 6'3" 177lbs, and it is easy to ride and gloriously fun.  I thought I would be buried with my Bultaco Pursang, but sold it.  Now I will be buried with my 2013 150SX.

It hits a little harder in the midrange due to a couple of more HP's there compared to a 125 there. But not as hard that i would say that it is a problem.

People should keep in mind that the sx150 is a purpose built 150 with exhaust, porting, stroke and ignition built for it. you get "stock bike" hours out of the piston etc and that nice stock bike powerband.

My latest build is a Honda cr144 -07 built for race gas, custom mapped ignition, different exhausts tested etc on the dyno. It puts out more power and torque on the dyno than a stock sx150 does, but when i ride it the sx150 feels more like a complete package in stock form than the Honda.

2018 KTM 150 is the most fun I've ever had on a motorcycle, including pit bikes and streetbikes. 

you either want a piece of junk or you want a yamaha, the choice is yours. If you can afford a 21 yz125, you can afford a 22 yz125. 

17-22 Carb’d Austrian 125/150. I’d try to ride both and see which you like more. I have both and prefer the 125 hand over fist in 90% of riding situations. I wouldn’t rule out the 2016 bikes either, the 4cs is garbage, but so is the early AER stuff IMO, so you’re spending money regardless on suspension. My 125 and 150 are both 2016s and each one has over 200 documented hours on the chassis. No transmission issues to count other than one that was self inflicted, do a crank at 100 hrs in each one before they go out, top end around 20 hours, and clutches as needed. The OEM baskets are good for around 100 hours or more depending on how you ride. The adjustable power valve and base gaskets make the engine fun to mess with if tinkering is your thing. Chassis are still tight after all this time. Really killer bikes once you get it right for you. 

I’d hold out for a 22+ Yamaha the newer ergos are worth it.

Another vote for Yamaha. I raced and won in the +30 B class on several different YZ125s. Those things are bulletproof and fast enough to get the job done. 

It’s hard to go against the Austrian brand as a vet rider when they have a 150 and a 350, even though I’ma Kawi guy at heart 😂 

Yeah, they have always been good on supplying bikes that the Japanese don’t. 

I rode KTM in 2007 but that was the first year with the new sx450 with electric start and that bike was a ticking bomb, mid season I switched to Honda and never looked back after several clutch and engine failures on the KTM.

After that I always said that the only time I would buy a KTM again was if I wanted a displacement that the big 4 don’t sell.

I also liked the exc 200 for woods riding back around 2006

I’d wait another 2 months just in case kawi comes out with a cool one. 

A TM144 would be the ultimate, but I just don’t want to spend that much. 

^^ this exactly, I even saw a commercial last January(2025)!

I’ve had all makes and models of 125s over the years as well as a few 150s. Always found the 150s to be really abrupt and hard hitting compared to a 125 that revs a lot longer.

Gone full nostalgia and bought the first 125 I ever had which is a 2004 125sx.

Probably not the best choice to be honest, but they look so cool and it holds good memories.

So with the 150 you are generally shifting more often to keep it in a narrower powerband ?

Yes, I find myself shifting much more on the 150 vs the 125. Once you’re in 3rd gear, the 125 will just keep pulling and pulling, in stock form they’re impressive. I had PC build my 125 motor and it is a missile but so easy to ride, sometimes it seems impossible for the power to fall off in 3rd, 4th and 5th. 

The 150 is great in certain conditions. We had a smaller track around here that was like a tamed down SX/AX track. Very four stroke friendly with big jumps right out of corners. The 150 was light years better and easier to ride if I didn’t want to case everything in site. When I went to my dad’s in WV and rode the Hatfield and McCoy trails, the 150’s torque was a huge advantage compared to the 125. Down here in FL for woods and Harescrambles I take the 125 everyday. Much better choice for the deep sand and long open fields we usually have on our tracks. 

The engines in those early 2000s KTM 125s were rockets, they just hadn’t found suspension and designed a chassis that was good enough to keep up with it. The ‘03 250SX is another good example. Unreal engine, everything else around it was terrible. 

Have a 2019 SX 36 hrs Has vital jetting vented side plate. Bike rips, still has original plastics. 4 sale in so cal if you want to road trip it. LMK

You should really look into having your 150 motor built by PC or twisted! I found my 150 even with good jetting had a very narrow Power Band mostly midrange it it was a lot of work to ride. Had Jamie do the full motor on it and it's insane how fast it is great bottom in very linear into the mid that just pulls and the top end that never stops it literally never stops pulling which is strange for a 150 the overrev is crazy it's absolutely so fun to ride now it's hard to keep my son off it LOL