Patched: Mikuni Bs25 Carburetor Diagram

The Mikuni BS25 is a small, slide-type carburetor commonly found on minibikes, small motorcycles, scooters, and custom builds. “Diagram patched” here means providing a corrected, annotated diagram plus step-by-step guidance for identifying components, common problem areas, and how to safely patch or repair typical faults (jets, floats, fuel leaks, vacuum ports, slide wear). This post gives a practical visual and procedural reference for hobbyists and mechanics.

The BS25 used on bikes like the YBR 125 has a vacuum port that connects to the fuel petcock (fuel tap). Clearly draw the vacuum line routing on your diagram. A common mistake is mixing up the fuel line and the vacuum line, which will prevent fuel from flowing.

Ignore the official part numbers at first. Look for colored ink, handwritten arrows, or digital callouts. These are your warnings. mikuni bs25 carburetor diagram patched

| Patch Type | Diagram Marking | Purpose | |------------|----------------|---------| | | Red circle around pilot jet | Replacement with larger jet (e.g., #42.5 → #45) | | Drilled passage | Dashed line added | Enlarging air bleed hole for richer idle | | Gasket repair | Cross-hatched area | Silicone or paper gasket patch for vacuum leak |

was choked with green oxidation [4]. The diagram pointed to the pilot circuit The Mikuni BS25 is a small, slide-type carburetor

If you’ve been wrenching on a scooter, dirt bike, or a small ATV (like the Yamaha Vino 125 or early Suzuki Burgman), you’ve likely met the Mikuni BS25. It’s a reliable, constant-depression (CV) carburetor, but it has a dirty little secret:

Print out a high-resolution exploded view of the BS25. While Mikuni doesn't publish a single consumer-facing PDF for this model, diagrams can often be found in service manuals for specific bikes like the Yamaha YBR 125 or Suzuki Intruder 125. The BS25 used on bikes like the YBR

The Mikuni BS25 is a 25mm Constant Velocity (CV) carburetor, frequently found on small-displacement Japanese motorcycles, ATVs, and older scooter models from the 1980s and 1990s. While known for smooth operation, the BS25 is susceptible to issues related to aging rubber components, clogged jets, and vacuum diaphragm failure.

To keep your Mikuni BS25 from needing a "patch" job in the first place, follow these steps:

Replacing the entire slide assembly is best, but a temporary patch can be made using specialized flexible rubber sealant (like Permatex Super Weatherstrip Adhesive or liquid tape) applied extremely thinly to the crack. Note: A patched diaphragm is temporary; replacement is recommended. Area 2: The Float Bowl Gasket Fix

If the pilot jet is stripped, soaked, or impossible to clean, it must be replaced. Cleaning often requires soaking the carburetor body in dedicated carburetor cleaner, like those found on Amazon, and using compressed air to clear the tiny passage under the pilot jet. The Diaphragm "Patch"