Small brass tube that controls fueling from idle up to 1/4 throttle. 3. Disassembly and Inspection Steps
: Disassemble and soak metal parts in a dedicated Carburetor Dip. Avoid soaking rubber O-rings or the vacuum diaphragm in harsh solvents, as they will swell or tear.
Keep carburetor cleaner away from the diaphragm, float bowl O-ring, and needle valve tip. Strong chemicals will swell or destroy these rubber components. mikuni bs26 carburetor manual verified
Mid-range throttle response (1/4 to 3/4 throttle) is managed by the jet needle. If your needle features multiple adjustment grooves, you can adjust the clip position:
| Symptom | Probable cause | Manual verification step | |---------|----------------|---------------------------| | Hesitation at 5000 rpm | Torn diaphragm | Visual inspection; blow lightly into vacuum port—slide must rise smoothly | | Hard start cold | Clogged starter circuit | Remove starter plunger; check tiny fuel passages with carb cleaner | | Rich idle (black plugs) | Pilot screw too far in | Reset to 2.5 turns out; replace pilot jet if >3.5 turns required | | Surge at steady throttle | Incorrect float height | Remeasure at 30° angle; adjust tang gently | | High idle (1800+ rpm) | Vacuum leak or stuck slide | Spray propane around intake boots; check slide for free movement | Small brass tube that controls fueling from idle
Use the idle thumb screw to drop the idle back down to factory specification (typically 1,400 RPM). Resolving Mid-Range Lean or Rich Conditions
Troubleshooting advice for a you are experiencing. Detailed steps on identifying and fixing vacuum leaks . Share public link Avoid soaking rubber O-rings or the vacuum diaphragm
An intake tract air leak, or an overly lean pilot circuit.
Hold the brass jets up to a light source. The internal holes must be perfectly round and free of debris. Never clean jets with steel wire, as it damages the soft brass. Use compressed air or nylon brush strands.