Mikuni Bs26 Carburetor Manual Verified [better] Info

| Specification | Verified Value / Range | | :--- | :--- | | | Constant Velocity (CV), 4-stroke | | Venturi Diameter | 26 mm (Primary oval), 22.2 mm (Secondary measurement for some models) | | Idle Speed | 1600 ± 100 rpm (Aprilia Leonardo 125) | | Main Jet (Primary) | #100 (Common stock on many 125-250cc engines) | | Pilot Jet (Primary) | #42.5 (Aprilia Leonardo 125) / #25 (Common for modded bikes) | | Jet Needle | 4DX8-3 or 4DX8-4 | | Needle Clip Position | 4th groove from the top (factory stock) | | Needle Jet | 0 (Primary) – The factory code is "0" (zero), but it also corresponds to a size of 0 (often P-0 or O-0) | | Air Jet | #135 (Main), #155 (Bypass) | | Float Valve Seat | 1 mm | | Float Height (Dry) | Varies by model, but generally measured with the carb upside down, just before the float needle spring is compressed. Consult your specific bike's manual for the exact millimeters. Common ranges for similar bikes are 6.2–8.2 mm or 11–13 mm. | | Float Weight | 8.6 g | | Fuel Level (Needle/Seat) | Factory preset; do not change arbitrarily. Leak-test at 5 PSI for at least one minute. |

Remove the jet needle from the center of the slide, noting the exact order of any plastic spacers, clips, or washers. Step 2: Float Bowl and Jet Removal

To verify and validate the information provided in this manual, we have consulted the following sources:

The Mikuni BS26 relies on engine vacuum to lift its slide. Understanding how these parts interact is critical for effective troubleshooting. mikuni bs26 carburetor manual verified

Manages the mid-range (1/4 to 3/4 throttle).

The metal cap houses a soft rubber diaphragm attached to the vacuum slide. Engine vacuum draws air through an offset hole in the bottom of the slide, pulling the slide upward against the return spring. 2. The Fuel Metering System

Standard operating idle is typically between 1,450 and 1,550 RPM once the engine has reached operating temperature. Maintenance and Rebuild Best Practices | Specification | Verified Value / Range |

Carefully lift the cover, noting that the diaphragm spring will push upward.

If you own a late-80s to early-2000s Suzuki GS500, GN250, or GZ250, you have almost certainly cursed the name of the —or perhaps you’ve praised its reliability. The truth is, this constant velocity (CV) carburetor is a masterpiece of emissions-era engineering when it works correctly. But when it fails? It becomes a ticking time bomb of hesitation, flat spots, and sticky slides.

Periodically check the rubber diaphragm for holes, cracks, or stiffness, as these will prevent the slide from lifting correctly. Float Height: | | Float Weight | 8

: Supplies a rich mixture for cold engine starts. 🔧 Step-by-Step Tuning Guide

Governs the fuel-air mixture at wide-open throttle.

Carefully unscrew the Main Jet and the recessed Pilot Jet . Use a precisely fitting flathead screwdriver to avoid stripping the soft brass.

Use a flathead screwdriver to unscrew the main jet and the deeply recessed pilot jet. Step 4: Cleaning and Chemical Treatment