MNNTHBX’s Pumped-Up Kawasaki Z125 Pro Track Tool

Modifying minibikes has a long and dubious history. From the highly customized Monkey Bikes of the '70s to the minimoto craze of the late '90s to the Grom fever that's still afflicting much of the world, folks seem all too eager to toss a wheelbarrow full of cash at affordable bikes in an effort to build something unique.

More power to them, I say, because as ridiculous as these customs may be, they’re always impressive. And this Z125 Pro is particularly exciting because it speaks directly to something I’m fond of: ripping around the track.

"We set out to build a full-tilt track weapon," says Greg Hatcher, head honcho at MNNTHBX, the parts and accessory company I profiled for a recent Wrench Room feature. "While the budget was unlimited, we chose to utilize standard product," Greg says.

Let’s start with some numbers. Yes, Hatcher more than doubled the Z125’s $3,000 MSRP, but trackbikes are always pricey, so don’t sweat the cost. What matters are the results of the investment. Stock, the Z125 makes about 8.5 hp and 6.5 pound-feet of torque. Greg’s Z125 is making 14.8 ponies and 10.5 pound-feet. Marinate on that for a moment. “It power wheelies in second gear,” Greg says. The video below, filmed at the Herrin Compound with pro rider Aaron Colton, confirms the Kawi’s performance. Then again, Colton can wheelie anything.

Boosting the power that substantially required a crank-up engine build. "Air enters the motor through the MNNTHBX Mtake and TB throttle body," Greg says, "and is processed through the TB 143 big-bore kit with a stroker crank, resulting in 155cc of displacement. Spent gases exit via a Yoshimura RS-2 exhaust. While the stroker crank adds major torque, a lightened primary gear keeps the throttle response ridiculously crisp. We've always had major success fueling with the Bazzaz Zfi, so we knew we'd go that route. What we hadn't done before was use its integrated quick-shift and traction control unit. The full throttle shifts really add to the potential aggression of the engine package."

After that, the guys updated the controls. They replaced the stock top clamp with a MNNTHBX billet clamp, which holds Renthal RC High Fatbar. Machined ASV levers replace the uninspiring stock pieces, and a G2 quick-turn throttle, Renthal grips, and Driven bar ends finish off the cockpit. In place of the stock foot controls, the Knoxville boys utilized Driven rearsets. I've used those same rearsets on a Grom, and they offer plenty of adjustment and great grip for your boots, though the footpegs are fragile. Or maybe I just crash hard. Jump to 2:10 in this video to see what I mean.

Dropping some weight was next on Greg’s list. “Beyond the diet provided by the exhaust and rearsets,” Greg says, “we replaced the OE battery with our LiPo, and since this is a dedicated trackbike, we ditched all factory lighting. Our MNNTHBX race plate kit tidies up the front end and retains the instrument panel.”

With 75 percent more power on tap, the little Kawi’s stock brakes weren’t going to hack it. OE stamped-steel discs were replaced by Galfer wave rotors, semi-metallic pads were slotted into the caliper, and the stock rubber brakes lines were replaced with stronger braided brake lines that won’t swell under heavy pressure. Suspension—which is pretty good from the factory—was made even better with an Öhlins drop-in fork kit and Öhlins shock.

With a few more details sprinkled in—a custom seat from Jettrim, powdercoated wheels, and lots of anodized bits—this Z125 is fully blinged out. And while plenty of customizers just aim to improve the appearance, I'm happy to see that Greg and his team put even more effort into the engine, brakes, and suspension. In my mind there's nothing dubious about this build, but as a track guy, I guess I'm biased.