Mikuni Bs25 Carburetor Diagram | Patched

Securely seals the upper vacuum area and holds the slide spring in place.

Meters fuel at wide-open throttle (WOT) (75% to 100% throttle).

Meters the initial air mixing with fuel for the idle circuit. mikuni bs25 carburetor diagram patched

The tiny O-ring on the mixture screw (air screw) often rots, causing erratic idling.

If the bike sits for more than two weeks, modern ethanol fuel will begin to degrade. Securely seals the upper vacuum area and holds

The Mikuni BS25 is a legendary 25mm CV (Constant Velocity) carburetor found on countless vintage small-displacement Japanese motorcycles, ATVs, and scooters from the 1970s through the 1990s. While known for reliability and efficiency, these carbs are now decades old. Age-related issues—like blocked air passages, hardened diaphragms, or stubborn varnish—require a comprehensive approach, often referred to as "patching" or restoring the carburetor to optimal performance.

Fine-tunes the idle fuel-to-air ratio. Note: On emissions-regulated models, this is often blocked by a metal plug that must be drilled out. Bottom Section: Fuel Storage The tiny O-ring on the mixture screw (air

Remove the four screws holding the top vacuum cap. Remove the cap, spring, and carefully lift out the slide and rubber diaphragm.