Mikuni Bs25 Carburetor Diagram Patched < 2026 Update >

The Mikuni BS25 is a constant vacuum (CV) carburetor commonly found on small-to-medium displacement motorcycles (e.g., Suzuki GN250, Yamaha SR250, early Kawasaki Z250). In workshop parlance, a “patched diagram” refers not to a software patch, but to a manually corrected, annotated, or repaired schematic—often used to overcome design flaws, wear, or tuning issues.

This report analyzes a “patched” version of the BS25 diagram, focusing on common failure points, aftermarket modifications, and how the patch alters original Mikuni engineering. mikuni bs25 carburetor diagram patched

The original diagram shows the pilot jet screwing into a blind hole. This is wrong. The Patch: A red circle or arrow connecting the pilot jet cavity to the three small bleed holes downstream of the throttle plate. The patched diagram highlights that fuel must travel horizontally through a tiny drilling that you cannot see without removing the mixture screw. The Mikuni BS25 is a constant vacuum (CV)

        [Choke Plunger] ──── [Enrichment Circuit]
                 │
    [Air Horn] ──┼── [Diaphragm Cover] ── [Vacuum Piston / Slide]
                 │           │                     │
    [Air Jet (Primary)] ─────┼───── [Needle Jet] ──┤
                             │                     │
    [Throttle Stop Screw] ──[Throttle Valve]       │
                             │                     │
    [Main Jet] ── [Emulsion Tube] ─────────────────┘
         │                    │
    [Float Bowl] ────── [Pilot Jet]
         │                    │
    [Drain Screw]        [Mixture Screw]
                               │
                          (Hidden behind anti-tamper plug)