Step up from the stock 125. Koso's kit brings a larger 61mm bore, taking the engine to about 170cc, with an 11.5:1 compression ratio meant to keep pump gas and everyday reliability.
🔍 Does this fit your bike?
Honda Grom 125, 2014-2020 and Honda Monkey 125.
Koso part number MB623002.
Not for 2021+ models.
⚠️ Before you order
No returns on performance parts — please double-check your model year and fitment before ordering.
You may need to modify your engine case to fit the larger cylinder.
Tuning, a gasket set and other supporting parts are recommended; installation is for experienced builders.
