Spray aerosol carb cleaner directly into the pilot jet passage, main jet passage, and pilot mixture screw hole. Verify that fluid exits through the small transition ports inside the bore.
If adjustments are necessary, carefully bend the small brass tang on the float arm. Do not press against the delicate needle valve tip while bending.
Remove float bowl, extract pilot jet, clear passage with solvent and compressed air. Dirty inlet valve seat or incorrect float height setting.
The rubber diaphragm responds to engine vacuum, lifting the plastic or metal slide.
This design prevents the engine from bogging down if you snap the throttle open quickly at low RPM. Complete Specifications Factory Standard Specification Main Jet #110 to #132.5 (Application dependent) Pilot Jet (Idle) #15 to #22.5 Pilot Screw 1.5 to 2.5 turns out from lightly seated Float Height 17.0 mm ± 1.0 mm Step-by-Step Disassembly mikuni bs26 carburetor manual verified
Check for "varnish" or green gunk caused by old ethanol fuel.
Spray carburetor cleaner through every passage, jet, and emulsion tube hole.
“The pilot screw controls fuel, not air.”
Never use wires, drill bits, or welding tip cleaners to clear brass jets. These tools will gouge the soft metal, permanently altering the hole diameter and ruining your fuel calibration. 4. Line Routing and Hose Connections Spray aerosol carb cleaner directly into the pilot
Turn the pilot screw in/out in 1/2 turn increments every 10 seconds until the engine reaches its highest, steadiest idle.
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Standard sizes range from #110 to #130 depending on the OEM application. Pilot Jet: Usually a #15 or #22.5.
The best manuals are the original equipment manufacturer (OEM) publications. For the most part, a dedicated "Mikuni BS26 manual" does not exist as a single publication. Instead, the data is contained within the specific motorcycle's factory service manual. Do not press against the delicate needle valve
Remove the screws securing the top cap. Hold the cap down firmly, as the internal spring is under tension. Remove the cap, spring, and the plastic spring seat.
The Mikuni BS26 is a 26mm constant velocity (CV) carburetor used widely in motorcycles, ATVs, and scooters. Renowned for its smooth throttle response and fuel economy, this carburetor relies on engine vacuum rather than a direct cable linkage to lift the throttle slide.
Blow compressed air through all channels to verify they are completely clear. Hold the jets up to a light source to confirm the internal holes are perfectly round and free of debris. 3. Reassembly & Adjusting Float Height
The Mikuni BS26 is a 26mm Constant Velocity carburetor utilizing a vacuum-operated diaphragm, commonly tuned with a pilot screw set 1.5 to 2 turns out. Key maintenance involves cleaning the jet circuits, checking for varnished fuel, and ensuring the float needle seats properly. For detailed schematics, view the Mikuni BS26 Manual on Scribd