As you would expect after 17 years of development, a modern KTM 125SX, and especially a 150SX, will make significantly more power than a big-bore 2003 YZ134.

Dear MXperts,

I would like your help. I am trying to decide on what my next bike should be and have narrowed it down to the KTM 125SX or KTM 150SX. I am a 44-year-old Vet Intermediate who weighs 170 pounds with no gear on. I have been riding and racing motocross for 20 years. I had a 2003 YZ125 that I bored out to 134cc and had the compression raised enough to require race gas. Then I switched to a 2005 YZ250, which I am still currently riding. I rode the YZ250 and YZ134 back to back, and my lap times were identical because my corner speed on the 250 was so bad. I still feel like I get too much wheel spin out of corners on my YZ250 when traction is minimal. I want to go back to a small-bore bike and, from everything I’ve read, it seems like the KTMs are the obvious choice. I’m just not sure which one I should get. I tend to lean towards the 150SX because of the power. Do you think the 2020 KTM 125SX might pump out the same horsepower as my YZ134?

That’s a very long question just to ask if a 2020 KTM 125SX would be as powerful as your 2003 Yamaha YZ134. You can relax. In stock trim your 2003 Yamaha YZ125 produced 31.8 horsepower at 11,200 rpm (with 15.2 pound-feet of torque). Even with a 134cc big-bore kit, your 2003 YZ134 would have been lucky to get to 35.5 horses.

Now for the answer! A modern KTM125SX makes 38 horsepower in stock trim (with 17.73 pound-feet of torque), while the KTM 150SX produces 41 horsepower (with 18.81 pound-feet of torque). Based on your age, weight and class, you will be better served by the KTM 150SX. It makes 2 to 3 more horsepower across the whole powerband than the KTM 125SX. The added torque will get your extra body weight out of the corners quicker, while the additional 6 horsepower (compared to your 2003 YZ134) will be a revelation on the starts. It’s amazing what 17 years of R&D can achieve.


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