The Honda Monkey JB05 is one of the most popular mini bikes around. Compact, reliable, aesthetic, it appeals to both mini 4-stroke enthusiasts and urbanites looking for originality. But if the original version is already endearing, it leaves a lot of room for improvement: power contained at 9.4 hp, saddle uncomfortable over time, exhaust line of some sort.
In this article, we present to you the preparation project for Honda Monkey JB05 vintage 2025, which combines three distinct interventions:
- Stage 1 engine preparation : 145 cm³ kit, camshaft, reinforced clutch
- Sports exhaust : Yoshimura Magnum GP carbon high pass
- Custom-made upholstery : Black Alcantara, cognac Pavinto, personalized embroidery
Three independent projects, but designed together for a coherent result from A to Z.
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Honda Monkey JB05 engine preparation: 145 cm³ kit, reinforced camshaft and clutch
The Honda Monkey JB05 leaves the factory with a 125 cc engine capped at 9.4 hp – sufficient for the city, but quickly limited when you're looking for character on the open road. Our Stage 1 engine acts on three levers simultaneously: displacement, distribution and clutch. Result: more torque exiting corners, more power at the top of the revs, and an engine capable of withstanding this increase in load over time.
145 cm³ Honda Monkey JB05 cylinder kit: more torque from mid-range
The Honda Monkey JB05 leaves the factory with a 125cc engine. The first lever for improvement is high engine kit 145 cm³, which replaces the original cylinder and piston with parts with higher dimensions.
Result: an increase in the combustion volume, and therefore in the torque available at low and medium revs. Concretely, the difference is felt as soon as you exit the corner: the bike picks up more clearly, without having to systematically downshift.
Compatibility: the kit is compatible with the original cylinder head of the JB05 (JB-03 / JB-05), which avoids touching the cylinder head - an essential characteristic of a clean Stage 1.
Kitaco sports camshaft: more power at the top of the revs
The camshaft manages the opening and closing of the valves. A Kitaco sports camshaft modifies the profile of the cams to lengthen the duration of valve opening and increase lift.
The direct consequence: better filling of the cylinder with an air/fuel mixture, therefore more power at the top of the revs.
Combined with the 145 cm³ kit, the sports camshaft creates a real synergy: the low speed gains torque thanks to the displacement, the high speed gains power thanks to the distribution.
High flow oil pump: longevity of the prepared engine
More power means more heat. The original oil pump of the Monkey JB05 is calculated for the stock engine. As soon as the displacement is increased and the distribution is changed, the engine heats up more, lubrication must follow.
The high flow oil pump ensures sufficient oil supply to moving parts, even under heavy load. It is a part often neglected in preparations, but which determines the longevity of the engine over time.
Reinforced clutch: billet machined plate and Kitaco springs
The increased torque generated by the 145cc kit and sports camshaft places additional pressure on the stock clutch. Without reinforcement, the clutch may slip when exiting a corner or deteriorate prematurely.
We installed a clutch pressure plate cut from solid (better rigidity, no deformation under load) as well as reinforced clutch springs to keep everything together even under conditions of strong acceleration.
Want a Stage 1 engine on your Monkey JB05?
Cylinder kit, camshaft, clutch — we take care of everything in our French workshop.
Project 2 — Exhaust: Yoshimura Magnum GP carbon high passage
The exhaust is an independent modification of the Stage 1 engine, it can be carried out alone or combined with an engine preparation. It is also the most visible and audible modification.
We opted for the Yoshimura Magnum GP for Honda monky JB-05, in carbon finish, high passage. Here is why this choice is consistent with the entire preparation:
- High passage : the silencer goes up along the frame rather than going down under the engine, which frees up space, slightly improves the center of gravity and gives an immediate sporty look.
- Carbon finish : maximum lightness, high thermal resistance, premium aesthetic. The woven carbon of the Yoshimura is instantly recognizable.
- JB05 Compatibility : the Magnum GP is specifically designed for the JB02, JB03 and JB05 versions of the Monkey — no need for adaptation.
- Power gain : the sports exhaust improves the evacuation of burnt gases, which naturally complements the work of the cylinder kit and the camshaft.
On the road, the sound is round, deep, without being aggressive. This is the sound signature of the seriously prepared mini 4-stroke.
Project 3 — Custom-made upholstery: black Alcantara, cognac Pavinto and embroidery
Custom-made upholstery is a project in its own right, completely independent of engine preparation. The original Honda Monkey JB05 saddle is functional but basic: firm foam, standard synthetic covering, with no customization possible.
We have completely redesigned the upholstery around a low-rise Kitaco base, modified in our workshop:
| Area | Material | Detail |
|---|---|---|
| Seated | Black Alcantara | Black on black honeycomb pattern |
| Sidewalls and outline | Pavinto cognac | Retro style, premium leather grain |
| Embroidery | Personalized | “Monkey” logo embroidered tone-on-tone |
| Topstitching | Tone on tone | Cognac thread on Pavinto, black thread on Alcantara |
The result is a tailor-made saddle that respects the retro spirit of the Monkey while integrating high-quality contemporary materials. The cognac Pavinto recalls the aged leather of vintage Japanese motorcycles from the 70s, while the Alcantara provides the comfort and support of a premium material.
Personalized “Monkey” embroidery is made in our motorcycle upholstery workshop in Abergement-Sainte-Colombe, France.
Your Honda Monkey deserves a unique saddle
Alcantara, Pavinto, embroidery, stitching — handmade in our French workshop.
From €299.99 · Delivery 5 to 10 days
From engine preparation to custom saddle: Transformation of Honda Monkey JB05 from A to Z
This project clearly illustrates the Nox Custom philosophy: motorcycle preparation is a whole. The Yoshimura exhaust, the 145 cc kit and the Alcantara/Pavinto upholstery are not independent elements, they form a coherent whole, designed to work together visually and mechanically.
Project Summary — 2025 Honda Monkey JB05:
Stage 1 engine preparation
- ✅ 145 cm³ cylinder kit
- ✅ Kitaco sports camshaft
- ✅ High flow oil pump
- ✅ Clutch plate cut from solid
- ✅ Reinforced clutch springs
Exhaust
- ✅ Yoshimura Magnum GP carbon high passage
Custom-made upholstery
- ✅ Low-cut Kitaco base modified in the workshop
- ✅ Black Alcantara seat with honeycomb pattern
- ✅ Pavinto cognac sides
- ✅ Personalized tone-on-tone “Monkey” embroidery
Have your Honda Monkey JB05 prepared at Nox Custom
Our workshop, based in L'Abergement-Sainte-Colombe in Saône-et-Loire (71), offers and installs the Kitaco, Takegawa, Yoshimura and Over Racing spare parts for Honda Monkey, Dax, MSX and GROM, as well as a custom motorcycle upholstery for all brands (Aprilia, BMW, Ducati, Harley-Davidson, Honda, Kawasaki, KTM, Suzuki, Triumph, Yamaha...). Installation assured in our workshop - no subcontracting.
Ready to transform your Honda Monkey JB05?
Free quote, response within 24 hours
Nox Custom — Specialist in upholstery and mini 4-stroke preparation in France. 17A Rue de Foichot, 71370 L’Abergement-Sainte-Colombe.