The Ultimate Mikuni BS26 Carburetor Manual & Tuning Guide The Mikuni BS26 is a 26mm constant velocity (CV) carburetor widely used on small-displacement motorcycles, ATVs, and scooters. Known for its fuel efficiency and smooth throttle response, it is a staple on machines like the Suzuki GN125, Yamaha Virago 250 (XV250), and various 125cc to 250cc Chinese imports.
Inspect the diaphragm rubber for splits. Ensure the slide moves up and down freely inside the bore without binding. Issue 2: Fuel Leaks From Overflow Tubes or Airbox
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Genuine Mikuni carburetors have "Mikuni Corp" cast into the slide side and "Made in Japan" cast above the float bowl seam. Avoid substitutes, as non-genuine jets often lack precise calibration. mikuni bs26 carburetor manual verified
Below is a compiled from the official OEM service data for the BS26 carburetor.
Remove the top cover to access the diaphragm and slide. Check the rubber diaphragm for cracks, tears, or pinholes. Verified tip: A damaged diaphragm is the #1 cause of poor performance.
Delivers a rich fuel-air mixture required for cold starts. It bypasses the throttle butterfly valve entirely. The Ultimate Mikuni BS26 Carburetor Manual & Tuning
┌────────────────────────┐ <-- Carburetor Body Gasket Surface │ || │ │ || │ │ ┌─┴┴─┐ │ │ │====│ <--------- Needle Valve Hook │ ┌┴────┴┐ │ │ │ ┌──┐ │ <--------- Float Tang / Metal Tab │ ┌───┘ │ │ └───┐ │ │ / │ └──┘ │ \ │ │ / │ │ \ │ [ ]==X====X X====X==[ ] <-- Float Pontoons │ │ │ <--- MEASURE HERE ---> │ <-- Target: 21.4mm Reassembling the Top Slide
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.
Controls idle and low-speed operation (up to 1/4 throttle). Throttle Valve: Regulates air intake and vacuum levels. Ensure the slide moves up and down freely
Understanding the location of each sub-system prevents common assembly errors.
Mikuni BS26 Carburetor Manual Verified: Complete Tuning & Service Guide
The Mikuni BS26 consists of three main sections. Each section serves a distinct purpose in fuel mixing.