: You'll need:
No single “official” standalone manual exists from Mikuni for the BDS26 alone; instead, the critical data is sourced from original and the rare Mikuni HSR/VM/CV tuning guides that include BDS26 supplements.
: Use a well-fitting flat-head screwdriver to remove the Main Jet , Pilot Jet , and Needle Jet .
✅ Only use genuine Mikuni BDS26 diaphragms. Aftermarket “universal” types often have incorrect shore hardness, causing erratic slide rise.
Locate the float hinge pin. Slide it out gently using needle-nose pliers or a small drift punch. mikuni bds26 service manual
Accurate float height ensures the engine does not starve for fuel at high RPM or overflow at idle.
Clogged pilot jets (very common), incorrect pilot screw settings, or air leaks in intake boots.
Check if the factory metal anti-tamper plug is still intact. If present, carefully drill a small hole in the plug, insert a sheet metal screw, and pull the plug out.
[ Caliper Gauge ] =========|========= | <-- Measure Distance +--------v--------+ | [ Float ] | +-----------------+ =======/ \========= <-- Gasket Surface (No Gaskets) / \ Install the new fuel valve seat, filter, and float needle. : You'll need: No single “official” standalone manual
Cause: Debris stuck in the needle valve, a worn rubber needle tip, or a heavy, fuel-logged float. Cause: Clogged pilot jet or a leaking vacuum diaphragm.
The following specifications are standard for the Mikuni BDS26 as used in common 250cc applications. Always verify against your specific bike’s factory service manual . Specification Main Jet (M.J.) #90 (Front), #87.5 (Rear) Pilot Jet (P.J.) Needle Jet (N.J.) Idle RPM 1,450 – 1,550 RPM Dry Float Height 6.2 mm – 8.2 mm (Standard: ~7.2 mm) Throttle Cable Play 0.5 mm – 1.0 mm 2. Disassembly & Cleaning
If your bike is hard to start or won't idle without the choke, this is a classic sign of a clogged pilot circuit, usually from old fuel or sitting for long periods. A thorough cleaning and rebuild (including the pilot jet and its passages) is the only permanent fix.
While Mikuni and Yamaha never published a standalone "Mikuni BDS26 service manual," all necessary information is contained within the official Yamaha Factory Service Manual (FSM) for your specific motorcycle model. That's where you'll find comprehensive sections dedicated to the BDS26 carburetor. Accurate float height ensures the engine does not
Reassembly follows the reverse order of disassembly. Lubricate O-rings with a light film of silicone grease or clean engine oil before installation. Setting the Float Height
JIS screwdriver (Crucial: Phillips will strip Mikuni screws) Metric socket set (7mm, 10mm, 12mm) Carburetor cleaner (spray and dip) Compressed air Small pick set
Push the emulsion tube back into the body from the top bore, ensuring proper alignment.