Mikuni Bs25 Carburetor Diagram
: Located in the float bowl, these maintain a constant fuel level. If the float is set incorrectly, the engine may run too rich or too lean.
The float rises with fuel level, closing the needle valve at the preset height (typically 15–17mm measured from bowl mating surface to float top). mikuni bs25 carburetor diagram
| Component | Location | Function | |-----------|----------|-----------| | | Upper bore | Moves up/down via vacuum; holds the jet needle. | | Diaphragm | Under top cover | Seals vacuum chamber; lifts throttle piston when engine vacuum rises. | | Jet Needle | Attached to piston | Tapers to control fuel flow through needle jet from 1/4 to 3/4 throttle. | | Needle Jet (Emulsion Tube) | In carb body, above main jet | Fuel+air emulsion passes through here; needle moves inside it. | | Main Jet | Inside float bowl (center) | Controls max fuel flow at full throttle (typically #97.5 to #105). | | Pilot Jet | Beside main jet (smaller) | Controls idle to 1/4 throttle (typically #35 to #42.5). | | Pilot Air Screw | On side of body (often capped) | Fine-tunes idle air/fuel mixture (turns out = richer). | | Float & Float Valve | Inside float bowl | Maintains constant fuel level; needle/seat stops overflow. | | Choke (Enricher) | On carb body | Adds extra fuel for cold starts; not a true air choke. | | Vacuum Port | Engine-side bore | Connects to petcock or PAIR system; some have vacuum cap. | : Located in the float bowl, these maintain
Attached to the bottom of the slide, this tapered needle controls the fuel flow in the mid-range (1/4 to 3/4 throttle). 2. The Carburetor Body and Throat | | Needle Jet (Emulsion Tube) | In
Based on its design, the Mikuni BS25 is susceptible to a few common issues:
If you have landed on this page, you are likely holding a vintage motorcycle carburetor, staring at a bench full of jets, springs, and brass fittings. You are searching for the —not just a blurry JPEG, but a clear, anatomical roadmap to understanding one of the most common constant velocity (CV) carburetors found on 125cc to 250cc bikes from the 1980s and 1990s.