2024 KTM 125SX 2-STROKE: FULL TEST

The 2024 KTM 125SX is the most technologically advanced 125cc motocross machine that KTM has ever produced with an electric starter, two optional pre-programmed maps that can be changed on the fly, electronic power valve, electric starter and a throttle-body fuel-injection system. Combined with all the other features like Brembo braking components, WP suspension, a tool-less-access airbox and hydraulic clutch, this has got to be the best 125cc made, right?

Well, let’s not get ahead of ourselves just yet, because with technological advancements almost always comes some bugs that need to be worked out. Compared to the previous generation, the 2024 KTM 125SX only retains the use of the WP fork assembly, Brembo braking hardware, wheel fitment, Magura hydraulic clutch actuator and a few other components.

Fuel injection, optional mapping and electric starters have finally made it to the 125cc motocross class.

The 2024 KTM 125SX features so many new items compared to the previous generation that it will make your head spin. The frame is all new with all-new styling throughout, new rear suspension, electric starter that eliminates the kickstarter altogether, the carburetor is gone and replaced by a throttle-body fuel-injection system. The electronic power valve is now wired directly into the EFI mapping, allowing port timing to be changed using information relayed from the throttle-position sensor, along with the engine’s rpm. A few shops, however, like Twisted Development and WMR Motorsports, have cracked the code to these locked CPUs.

Spark advancement and fuel delivery are also able to be altered by the two preset maps installed at the factory, which can be changed on the fly using the handlebar-mounted switch. KTM then locked the CPU so the general public cannot alter any settings.

ktm has two mapping options from the factory but the stock ecu — KTM has two mapping options from the factory, but the stock ECU is locked and can’t be reprogrammed—at least for the time being

The carbureted, kick-start model tipped the scales at 195 pounds without fuel, making the Austrian 125cc machine the lightest, but with the addition of electric start and fuel injection, the KTM gained weight and is now hitting the scales at 206 pounds. In the small-bore two-stroke class, 11 pounds can make a huge difference.

What does it all mean? Fuel injection has definitely changed the power characteristics of the KTM 125SX. As a matter of fact, it completely flipped it over compared to the carbureted model. On the track, power feels like it starts sooner on the bottom, pulls about the same in the mid-range—although, it is less exciting—and then signs off earlier on the top end.

Just like when four-stroke motocross bikes switched over to fuel injection, the two-strokes are losing that signature hard hit of the powerband that everyone is used to and now produce a smoother, linear-type power. Most two-stroke purists will not be happy about this.

If you live and die by dyno charts, the new fuel-injected 125 model comes up about 3 to 4 horsepower short of the carbureted model’s peak horsepower. Although not as drastically different as the four-stroke model’s mapping options, all our test riders prefer the more aggressive (white) over the standard (green) options.

Starting a 125cc machine is not something most of the world thinks twice about, so having the magic button is always preferred. Overall handling is slightly stiffer than the previous model due to the rigidity increases in the new frame, but suspension settings seem to be a little softer, soaking up any harsh feeling back to the rider.

the carbureted kickstart model the fuel injected electric start model — Compared to the carbureted kickstart model, the fuel-injected electric-start model is just over 10 pounds heavier and a few horsepower less at peak output, but it is easier to keep in the meat of that power.

If you are a serious racer in the intermediate or pro division, the 2024 KTM 125SX might not be the smart first choice for a couple of reasons. But, for the average 125cc pilot, this bike is easier to keep in the meat of the power, has an electric starter, the guessing game of jetting is eliminated by fuel injection, mapping options are on the fly, has great brakes and an overall handling package that fits a wide variety of riding skill levels. You just have to be honest with yourself about what you are looking for.