Before making modifications, baseline your carburetor using the verified factory specifications. While specific jetting varies slightly by vehicle manufacturer (such as Suzuki or Yamaha), standard baseline values provide a reliable starting point. Factory Specification / Measurement Main Jet (Stock) #110 to #132.5 (Application dependent) Pilot Jet (Stock) #15 to #22.5 Pilot Air Screw 1.5 to 2.25 turns out from lightly seated Float Height 17.1 mm ± 1.0 mm (Measured from gasket surface) Fuel Level 4.0 mm ± 0.5 mm below the bowl mating surface Idle Speed 1,300 – 1,500 RPM (Typical engine baseline) 2. Component Diagram and Anatomy
Proper maintenance requires specific tools and a systematic approach to avoid damaging internal brass components. Verified Tool List: JIS (#2 & #3) Screwdrivers:
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.
[ Top Cover ] │ [ Diaphragm Spring ] │ [ Vacuum Diaphragm ] ─── [ Jet Needle ] │ [ Carb Body ] ──────── [ Butterfly Valve ] │ ┌─────────┴─────────┐ [ Pilot Jet ] [ Main Jet ] └─────────┬─────────┘ [ Needle Jet ] │ [ Float Valve ] │ [ Float ] │ [ Float Bowl ] mikuni bs26 carburetor manual verified
Manages the mid-range (1/4 to 3/4 throttle).
Hold the rubber slide diaphragm up to a bright light. If you see any light through the rubber, it must be replaced.
Set the idle speed screw to factory specification (typically 1,300–1,500 RPM). [ Top Cover ] │ [ Diaphragm Spring
Spray the exterior with aerosol carburetor cleaner to prevent dirt from entering the internal circuits during disassembly. Step 2: Diaphragm Inspection (Top Section)
| Part | Mikuni OEM number | |------|-------------------| | Pilot jet (#35, #38, #40) | N151.067 (series) | | Main jet (#97.5, #102, etc.) | N100.604 (large round) | | Float needle & seat | VM28/486 | | Float bowl gasket | BS26-001 (generic) | | Diaphragm (complete slide assembly) | 13229-45210 (Suzuki) / N224.213 |
These settings are for a stock, unmodified engine at sea level. If no leak exists
Connected directly to your throttle cable. Controls airflow entering the engine intake manifold.
With the engine warmed up, adjust the screw for the highest, smoothest idle. If the idle hangs, the mixture is too lean; if it's sluggish, it's too rich. B. Idle Speed Adjustment Standard: The idle speed should generally be set to RPM, depending on the engine model. C. Jetting and Needle Position
Spray carburetor cleaner around the rubber intake manifold while the engine runs. If the RPM changes, replace the leaking manifold or O-ring. If no leak exists, back the pilot mixture screw out an additional 1/4 turn.