Mikuni - Bs26 Carburetor Manual Verified

5D-series (Clip typically non-adjustable on stock EPA models)

The BS26 operates on a variable venturi design where a vacuum-operated diaphragm controls the slide lift, ensuring smooth throttle response across various engine speeds. Most tuning issues originate in one of five metering systems:

“You need to drill out a plug to adjust the pilot screw.”

Specifications:

Understanding the anatomy of the CV carburetor simplifies the troubleshooting process.

| Specification | Verified Value | Notes | | :--- | :--- | :--- | | | #127.5 (Left) / #130 (Right) | GS500 only. Singles use #125. | | Pilot Jet | #40 | (Some models use #37.5 – check your needle) | | Pilot Air Screw | 2.5 to 3.0 turns out | From fully seated. Do not exceed 4 turns. | | Float Height | 13.0 mm (13.7 mm for GN250) | Measure with carb inverted, float tang just touching needle spring. | | Needle Clip Position | 4th groove from top | (Standard is middle, but GS500 uses richer 4th) | | Idle Speed | 1,200 RPM (+/- 100) | Must be set when engine is fully hot. | | Diaphragm Part # | 13258-02C00 | (OEM Mikuni – Aftermarket fails quickly) | | Float Bowl Gasket | 13269-01A00 | Not reusable after soaking in cleaner. |

The BS26 is a constant-velocity (CV) carburetor with a 26mm throat diameter. mikuni bs26 carburetor manual verified

For the best results, tune the circuits in a specific order. Start with the pilot circuit, then move to the needle, and finish with the main jet.

Invert the carburetor so the float tang just touches the needle valve spring (do not compress the spring).

Standard operating idle is typically between 1,450 and 1,550 RPM once the engine has reached operating temperature. Maintenance and Rebuild Best Practices Singles use #125

If the reading is not , gently bend the small metal tang on the float arm to adjust. Step 3: Inspecting the Diaphragm

For a standard Mikuni BS26 setup, technicians typically rely on these verified baseline settings:

Located on the engine side, pointing upward or downward. It controls idle fuel volume. | | Float Height | 13