In December 2022, Japanese performance parts and accessories maker Kitaco introduced two big bore kits for the Honda CT125 Hunter Cub. Enthusiasts looking to upgrade could choose between a 164cc or a 181cc kit, each including a cast aluminum cylinder, piston, piston rings, gaskets, I-map injection controller, oil cooler, and basically everything you would need to complete the conversion.  

That’s cool if you have a CT125 that you want to upgrade, but what if you have a different Honda 125? Say, a Monkey or a Grom? Fret not, friends, because as of August 2023, Kitaco has you covered as well. The company offers a range of bore-up kits for the Monkey and the Grom (or MSX 125), depending on your budget and what you want to accomplish. 

Kitaco has Tuning Menu pages set up for each bike on its site, showing you what options are available for your specific model. If you visit it close to the time of writing on August 16, 2023, you’ll find that both Grom (JC61 and JC75) and Monkey owners can choose between a 125cc high compression piston, a Light 164cc or 181cc big bore kit, a Neo 164 or 181cc big bore kit, and a completely over-the-top dual overhead cam 181cc big bore kit. 

Gallery: Kitaco Big Bore Kits for Honda Grom and Monkey

Unlike previous kits that Kitaco has sold in the past, the Light and Neo kits don’t come with the supporting high-performance camshaft and large capacity fuel injectors. Instead, those must be purchased separately—though Kitaco does offer those for sale, as well. You can also purchase the I-Map controller with wiring harness to adjust fuel injection mapping as needed as a separate item. Thankfully, the I-Map controller does not require any wiring modifications on the bike to work—it's just plug-and-play. 

Concerned about aesthetics? Kitaco offers both the 164cc and 181cc big bore kits in your choice of black or silver cylinders. The 164cc light big bore kit is priced at ¥17,600 (about $121) including tax for the black one, or ¥16,500 (about $113) including tax for the silver one. Bump up to the 181cc regular kit and it’s ¥18,700 (about $128) with tax for the black one, and ¥17,600 (about $121) for the silver one.  

The dual overhead cam 181cc big bore kit comes with an entirely new cylinder head with reshaped ports, larger valves, camshaft, piston, piston rings, hardware, and gaskets. Is it about as bonkers as you can get with a Monkey or Grom without doing an engine swap? Possibly. The price, as you might guess, also reflects this. It’s only available in silver, and the cost is ¥275,000 (about $1,886) including tax. 

It’s worth noting that Kitaco also offers instructions for its kits in both Japanese and English, which makes them more easily accessible to a wider audience of Honda minimoto enthusiasts.

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