Original factory diagrams often omit:
The patched version above merges exploded views from Suzuki GN250, Yamaha XV250, and Keihin-Mikuni cross-reference sheets to give you a complete, usable map for cleaning and tuning.
Original: In many diagrams for emissions-controlled models, the mixture screw is missing entirely. The Patch: A "cut here" dashed line over a brass plug on the underside of the carb, with an arrow pointing to the screw underneath. This is the most common "patch" added by home mechanics.
If you want, I can produce a printable annotated visual diagram (PNG/SVG) showing parts labeled as above — tell me whether you prefer a labeled schematic or exploded view and I’ll generate it.
You're looking for a detailed diagram of the Mikuni BS25 carburetor, specifically a patched or modified version. I'll provide you with some general information and point you in the right direction.
Mikuni BS25 Carburetor Overview
The Mikuni BS25 is a popular carburetor model used on various motorcycles, scooters, and ATVs. It's a reliable and efficient carburetor known for its simplicity and ease of tuning.
Diagram and Schematic
Unfortunately, I couldn't find a publicly available, patched diagram of the Mikuni BS25 carburetor. However, I can guide you to some resources that may help: mikuni bs25 carburetor diagram patched
Components and Parts
Here's a basic outline of the Mikuni BS25 carburetor components:
Patched or Modified Diagram
If you're looking for a patched or modified diagram, it's likely because you're trying to modify or tune your carburetor. When working with carburetors, it's essential to understand the basics of how they function and to take necessary safety precautions.
Tuning and Modification
When tuning or modifying your Mikuni BS25 carburetor, keep in mind:
If you're not experienced with carburetor tuning or modification, consider consulting a professional mechanic or a small engine repair specialist.
Additional Resources
For further assistance, you may want to consult:
The Mikuni BS25 is a Constant Velocity (CV) carburetor commonly used on vehicles like the Yerf Dog Scout, Rover, and some Yamaha motorcycles (such as the YBR 125). Unlike standard round-slide carbs, it uses a vacuum diaphragm to lift the slide, smoothing out throttle response. Key Components of the Mikuni BS25
Based on typical BS-series CV carburetor diagrams, these are the primary parts you will find: Upper Section (Vacuum Chamber): Top Cover:
Secured by two or four screws; holds the diaphragm assembly in place. Vacuum Diaphragm:
A rubber membrane that uses engine vacuum to lift the slide. Slide Spring: Returns the slide to the closed position when vacuum drops. Jet Needle (Slide Needle):
Attached to the bottom of the slide; it moves inside the needle jet to control fuel flow at mid-throttle. Main Body: Slide (Vacuum Piston): The vertical part moved by the diaphragm. Throttle Butterfly Valve:
The disc at the rear of the carb operated directly by your throttle cable. Pilot (Idle) Screw:
Often found on the side or bottom, used for fine-tuning the idle mixture. Bottom Section (Float Bowl): Float & Needle Valve: Controls the fuel level inside the bowl. Regulates fuel flow at wide-open throttle (WOT). Pilot Jet: Controls fuel flow at idle and low speeds. Float Bowl Gasket: Seals the bowl to the main body to prevent leaks. Visual Reference Original factory diagrams often omit:
Here are diagrams and exploded views of Mikuni BS and similar series carburetors to help identify these parts: 15+ Mikuni Motorcycle Carburetor Diagram Carburador Mikuni BS25 | PDF Sudco Intl. Corp. - Mikuni Diagrams Mikuni Carburetor Tuning, by Victory Library Victory Library
Carburetor - Mikuni BS25 Series Round Slide – VMC Chinese Parts VMC Chinese Parts
If you are knee-deep in a carburetor rebuild for a vintage scooter, a Japanese utility quad, or a small-bore motorcycle, you have likely encountered the notorious Mikuni BS25. This constant velocity (CV) carburetor is known for its reliability when clean, but absolute misery when clogged.
However, searching for a standard exploded view often leads to confusion. You may have stumbled upon the term "Mikuni BS25 carburetor diagram patched." This is not an official Mikuni document, but a community-driven modification to the original schematic.
In this article, we will dissect why the original diagram fails, what the "patched" version corrects, and how to use this hybrid diagram to fix your engine’s idle, flat spots, and fuel leaks.
| Symptom | Unpatched Diagram Diagnosis | Patched Diagram Diagnosis | | :--- | :--- | :--- | | Flooding gas | Replace float needle | Replace the hidden o-ring behind the seat (patch #2) | | No idle | Clean pilot jet | Clean the horizontal passage between pilot jet and mixture screw (patch #1) | | Bogs at half-throttle | Replace diaphragm | Check diaphragm tab alignment and spring placement (patch #4) | | Mixture screw does nothing | Unscrew further | Drill out the brass anti-tamper plug (patch #3) |
When rebuilding a BS25: