Reassemble the carburetor in the reverse order of disassembly, paying close attention to tolerances. Float Height Measurement
The is a constant-velocity (CV) downdraft carburetor commonly used on V-twin motorcycles, most notably the Yamaha XV250 Virago (and its V-Star 250 successor) and the Hyosung GV250 . While there is no single standalone "service manual" authored solely by Mikuni for this specific model, comprehensive maintenance data is found within the vehicle-specific service manuals for these motorcycles. Technical Specifications
Carb cleaner dip/ultrasonic cleaner (Optional but recommended) Rebuild kit (Diaphragms, O-rings, jets) 3. Removal & Disassembly Remove the fuel tank and drain fuel.
Spray carb cleaner through all passages. Use compressed air to blow them out.
Do not attempt to remove the carburetor cap screws without first releasing spring tension. Internal components (vacuum piston, metering needle, spring) are under light preload. Sudden disassembly may result in lost parts or diaphragm damage. mikuni bds26 service manual
Note: Brass is soft. Do not overtighten or you will strip the threads. Troubleshooting Common Mikuni BDS26 Issues Probable Cause Corrective Action Stuck float or worn needle valve Clean needle seat or replace float needle Hanging idle / Slow return Lean condition or vacuum leak Check intake boots for cracks; enrich pilot screw Bogging under acceleration Torn slide diaphragm Replace the rubber diaphragm slide assembly Starts only with choke on Clogged pilot jet Remove pilot jet and clear with thin wire or replace
Given that these carburetors are older, regular maintenance and occasional rebuilding are necessary to ensure proper operation. This guide serves as a comprehensive overview, covering disassembly, cleaning, assembly, and tuning. 1. Mikuni BDS26 Specifications & Components
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Install new pilot and main jets if your rebuild kit includes them. Reassemble the carburetor in the reverse order of
Target . Bend the small metal tang slightly to adjust if out of specification.
13.0 mm to 14.0 mm (Measured from the gasket surface) Idle Speed: 1,300 – 1,400 RPM
During assembly, ensure the slide housing o-ring is seated correctly. Because the recess is shallow, some builders use a fuel-resistant gasket cement like Permatex #85420 to keep it in place.
Before beginning, ensure you have a clean workspace and a carburetor rebuild kit containing fresh O-rings, gaskets, and a new needle valve. Use compressed air to blow them out
+-------------------------------------------------------------+ | MIKUNI BDS26 JET ASSEMBLY SEQUENCE | | | | [Slide Venturi Bridge] | | ^ | | | (Pushes up through top) | | +---------------+ | | | Emulsion Tube | <-- (Needle Jet / Holder) | | +---------------+ | | ^ | | | (Threads into bottom of holder) | | +---------------+ | | | Main Jet | | | +---------------+ | +-------------------------------------------------------------+ 1. Setting Factory Float Height
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Usually due to clogged pilot jets or improperly adjusted idle mixture screws.
Inspect the rubber diaphragm for pinholes by holding it up to a strong light source. 2. Disassembling the Float Bowl Flip the carburetor upside down. Remove the four bowl screws.