Mikuni Bs25 Carburetor Diagram Patched [new] | Direct

The "patched" diagram for the Mikuni BS25 carburetor is a legendary piece of mechanical lore, born in the early 2000s on greasy-fingered internet forums. It wasn't a factory update, but a community-led "patch" to fix a notorious design flaw in the pilot circuit that caused a lean-stumble on mid-range cruisers like the Yamaha Virago 250. The Origin Story

The Mikuni BS25 is a 25mm round slide carburetor, commonly used in GY6 150cc 4-stroke engines and certain Yamaha or Suzuki small-displacement bikes. Essential Resources & Diagrams mikuni bs25 carburetor diagram patched

Throttle Slide (Round): Moves vertically to control air inflow. The "patched" diagram for the Mikuni BS25 carburetor

Mixture Screw: Located on the side or bottom to adjust the air-fuel ratio at idle.  Common "Patched" Issues & Fixes  Air jet Pilot jet Main jet Needle valve

3. What Does “Patched” Mean Here?

The term “patched” on a diagram indicates one of three real-world interventions:

• Air jet
• Pilot jet
• Main jet
• Needle valve
• Float bowl
• Idle circuit
• Main circuit

3. The Mixture Circuit (Most Commonly Patched Mistake)

• Mixture Screw Location: On the BS25, the screw is air screw type (fuel metered by pilot jet, screw adjusts air bleed). Turning it out leans idle.
• Anti-Tamper Plug: Factory covers the mixture screw. Patched diagram note: Remove the aluminum plug (drill carefully) to access the screw—essential for tuning.

Conclusion

Decoding the Mikuni BS25 Carburetor: The Ultimate Guide to the “Patched” Diagram

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.