Yamaha YBR 125 bore kits 150 175

Yamaha YBR 125 for sale on Ebay UK

Yamaha YBR 125 parts for sale on Ebay UK

Yamaha YBR 125 workshop manuals on Ebay UK

Safety Message: Installing a big bore kit is a major mechanical modification that can affect the reliability, cooling requirements, and legal status of your motorcycle. Ensure you are familiar with engine teardown procedures and check local regulations regarding engine displacement changes and insurance.

Yamaha YBR 125 Big Bore Kits (150cc & 175cc)

The Yamaha YBR 125 Bore Kits post explores performance upgrades designed to increase the displacement and power of the standard 125cc engine.

Key Highlights:

Available Options: The post discusses the availability of 150cc and 175cc kits. The 150cc kit is a popular choice for those looking for a manageable power boost.

Potential Benefits: These kits aim to improve top speed and acceleration, providing a more capable ride for commuting or longer journeys.

Installation Considerations: While the post mentions future plans for a detailed fitting guide, users should be aware that such modifications typically require replacing the cylinder and piston.

Sourcing: At the time of the post, 150cc kits were readily available on platforms like eBay and Amazon, whereas 175cc kits were noted as more difficult to find.

Search Description

Information on 150cc and 175cc big bore kits for the Yamaha YBR 125, including potential performance gains and availability of aftermarket engine upgrade components.

i have just found these on Ebay uk , not tried one myself but someone might be interested i have heard good things about these kits but ive not tried first hand .

ill be fitting one of these in the future and trying them out for myself and ill do a post on fitting it and any improvements in speed etc it achieves .

if anyone can add any information please do so in the comments below .

Yamaha YBR 125 150cc bore kit  heres a link to buy one of ebay uk

or buy from Amazon UK here 

not yet found YBr 125 175 kit but if i do ill link it .

Safety Message: Big bore kits significantly alter engine thermals and fuel requirements. Running a modified engine "lean" (insufficient fuel) can cause overheating, piston seizure, or melted valves. Always perform a "plug chop" (inspecting the spark plug color) after installation to ensure the air-fuel mixture is correct.

Yamaha YBR 125 150cc Tuning & Fuel Adjustments

When upgrading a YBR 125 to 150cc, the most critical step is adjusting the fuel delivery to match the increased displacement.

1. For Fuel-Injected (FI) Models (2007–2016+)

Self-Adjustment: The stock ECU has a limited range of "self-correction" using the O2/Lambda sensor. While some riders report the bike runs okay with a 150cc kit, it often runs slightly lean at high RPMs because the stock injector and fuel map aren't designed for 150cc.

Upgrades: To optimize performance, professional tuners recommend an aftermarket fuel controller (like a Power Commander or similar FI adjuster) to richen the mixture.

Injectors: Some owners swap to a slightly higher-flow injector (e.g., from a Yamaha R15 or 160cc/min spec) to prevent the injector from reaching 100% duty cycle.

2. For Carburetor Models

Jetting: You must increase the size of the main jet. A common starting point is to go up 5–10% from the stock main jet size (e.g., if stock is #100, try #105 or #110).

Idle Mixture: The pilot air-fuel screw typically needs to be adjusted (usually turned anti-clockwise to richen) to prevent "popping" on deceleration, which is a common sign of a lean mixture after a bore kit install.

Spark Plug: Switch to a slightly "colder" spark plug (e.g., NGK CR8E instead of CR7E) to help dissipate the extra heat generated by the larger piston.

3. Mechanical Tips for the 150cc Kit

Compression: Many kits (like the Airsal 150cc) increase the compression ratio. It is highly recommended to use high-octane fuel (97/98 RON) to prevent "pinking" or engine knocking.

Gearing: Since the 150cc kit provides more torque but doesn't necessarily increase the RPM limit, many riders install a 15-tooth front sprocket (up from the stock 14) to take advantage of the power and achieve a higher top speed.

see more Yamaha YBR 125 blog posts