Mikuni Bds26 Service Manual -

Connects the main fuel line from the petcock/pump.

The is a 26mm downdraft, vacuum-piston (CV) carburetor designed to offer smooth acceleration and consistent fuel management. Proper maintenance is critical for performance, as these units can suffer from clogging due to ethanol-mixed fuels.

Must include a high-quality float seat, needle, bowl gasket, and fresh O-rings.

Comprehensive Mikuni BDS26 Go to product viewer dialog for this item. Service Manual Guide: Rebuild & Tune The Mikuni BDS26 Go to product viewer dialog for this item.

Secures the pull/push throttle cables.

Invert the slide to drop out the plastic needle retainer, the small spring, and the jet needle. Note the position of any tiny e-clips or plastic washers on the needle. Step B: Float Bowl Disassembly

Spray the exterior thoroughly to prevent dirt from entering during disassembly.

Ensure the alignment tab of the rubber diaphragm fits perfectly into the corresponding recess groove on the top rim of the carburetor body.

If you encounter a specific issue not covered in the manual, the community of fellow owners is an invaluable resource. mikuni bds26 service manual

Indicates mid-range issues (needle position or clogged emulsifier). High RPM Miss: Indicates main jet issues.

| Temperature | Altitude | Main Jet | Pilot Jet | Air Screw (turns out) | |-------------|----------|----------|-----------|------------------------| | -10°C to 0°C | 0-3000ft | 135 | 25 | 1.75 | | 0°C to 10°C | 3000-6000ft | 130 | 22.5 | 2.0 | | 10°C+ | 6000ft+ | 125 | 20 | 2.25 |

Torn diaphragms or dirty carburetor slides (causing them to stick).

Before turning a single screw, it is vital to understand the internal architecture of the BDS26. Factory Baseline Specs (Yamaha XV250 Reference) Connects the main fuel line from the petcock/pump

Modern ethanol fuel causes internal corrosion and clogged pilot jets if left sitting. Use fuel stabilizer.

Once reinstalled on the engine, the Mikuni BDS26 requires fine-tuning under operating temperatures. Diagnostic Matrix Probable Cause Corrective Action Stuck float or worn needle valve seat O-ring Clean float chamber, replace float needle valve. Engine hangs at high idle Hanging slide or vacuum leak at boot intake Check diaphragm seating; check intake boots for cracks. Backfiring through intake Lean pilot circuit mixture Back out the pilot mixture screw 1/4 turn at a time. Bogs down under load Clogged main jet or torn vacuum diaphragm Clear main jet with compressed air; replace diaphragm. Idle Mixture Optimization

Gently pull the rubber diaphragm and plastic slide upward out of the carburetor body.

Standard sizes range from #87.5 to #90 depending on the cylinder (front/rear). Pilot Jet: Typically #20. Must include a high-quality float seat, needle, bowl