Attaches to the center of the slide and meters mid-range fuel. The Middle Section (Carburetor Body) Venturi: The 26mm neck that accelerates airflow.
Hold the carburetor upside down at a 45-degree angle so the float tang rests lightly against the needle valve spring-loaded pin without compressing it.
Includes a lightweight plastic or brass float pivot-mounted to a brass needle valve. The needle seats into a replaceable or cast-in brass inlet seat to shut off fuel flow when the bowl is full. Step-by-Step Rebuild and Inspection Protocol
Hold the carburetor upside down. Tilt it at a 45-degree angle until the float tongue just makes contact with the spring-loaded pin of the needle valve, without compressing the pin's internal spring.
Troubleshooting advice for a you are experiencing. Detailed steps on identifying and fixing vacuum leaks . Share public link mikuni bs26 carburetor manual verified
Set the screw exactly halfway between those two problem points. This yields the highest, smoothest idle speed. 3. Tuning the Needle and Main Jet (25% to 100% Throttle)
| Modification | Required change | Jet size change | |--------------|----------------|------------------| | Pod filter (no airbox) | Impossible to tune well – BS26 needs airbox restriction | +2 on main jet, raise needle 1 clip, pilot +2 sizes – but still runs poorly | | High-flow exhaust | Usually none | Only if popping on decel → +1 on pilot jet | | High altitude (>2,000m) | Drop main jet by 1 size per 1,000m | Example: #100 → #95 |
Use a digital caliper or a specialized float gauge to measure the distance from the gasket mating surface (without the gasket installed) to the highest point of the float.
If you are working on a different model, the service manual for that specific motorcycle will be your best source for verified BS26 information. The aftermarket "BS series Operation Manual" on sites like mans.io may provide a more general overview of the BS carburetor family. Attaches to the center of the slide and
Gently turn the pilot screw clockwise until it lightly seats. Do not overtighten, or you will snap the fine tip off inside the carburetor body.
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Once inside, the rubber diaphragm is the most critical and fragile component. An inspection requires great care:
A common starting point is 1.5 to 1.75 turns out from a lightly seated position. Includes a lightweight plastic or brass float pivot-mounted
This is a classic symptom of a lean condition . The most common culprit is clogged pilot jets. Cleaning the pilot jet and its corresponding small orifices with carb cleaner and compressed air is the first verified solution.
| | Likely Cause | Recommended Action | | :--- | :--- | :--- | | Engine won't start | No fuel in float bowl, clogged pilot jet, or faulty choke/enricher | Check for fuel delivery, remove and inspect the pilot jet, and verify the choke/enricher plunger operates freely. | | Runs rich (black smoke, poor fuel economy) | High float level, oversized main jet, or fuel screw open too far | Verify and adjust float height. Test leaner main jet sizes. Turn fuel screw in to lean idle mixture. | | Runs lean (backfiring, hesitation) | Vacuum leak, low float level, undersized main jet, or fuel screw set too lean | Carefully spray starting fluid around the intake manifold to check for air leaks. Adjust float height. Test richer main jet sizes. | | Uneven idle, stalls | Clogged pilot circuit, improper pilot screw adjustment, or vacuum leak | Clean pilot jet and its passageways thoroughly. Re-adjust the pilot screw. Inspect carburetor and intake manifold gaskets. | | Poor acceleration, flat spot | Incorrect needle height setting, clogged main jet, or faulty diaphragm | Move needle clip to richen mixture. Clean or replace main jet. Inspect vacuum slide diaphragm for tears or pinholes. | | Engine revs but has no power | Worn or torn vacuum diaphragm, severely restricted air filter | Remove and carefully inspect the rubber diaphragm. Replace if damaged. Clean or replace the air filter element. |
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