Bs26 Carburetor Manual Verified: Mikuni

| Symptom | Common Forum Advice | | | :--- | :--- | :--- | | Hesitation at 1/4 throttle | "Turn the PAS to 4 turns." | Wrong. Replace the pilot jet (#40) and set PAS to 2.5 turns. 4 turns means the pilot jet is clogged. | | Backfire on decel | "You have a header leak." | Check the mixture screw O-ring. If it is flat or missing, you have an unmetered air leak. Replace the O-ring (Part # 13373-43580). | | Slide won't rise | "Buy a stronger spring." | Check the diaphragm vent hole. On the air filter side of the carb, there is a tiny 1mm passage. If clogged, the slide cannot sense vacuum. Blow it out with compressed air. | | Rich idle, black smoke | "Lower the needle clip." | Check the float needle seat. The BS26 has a removable seat with a built-in filter screen. If the screen is torn, debris holds the needle open. Inspect with a bright light. | Part 6: Tuning for Modifications (Exhaust & Pod Filters) Here is the harsh truth verified by decades of dyno runs: The Mikuni BS26 absolutely hates pod filters.

If you own a late-80s to early-2000s Suzuki GS500, GN250, or GZ250, you have almost certainly cursed the name of the Mikuni BS26 —or perhaps you’ve praised its reliability. The truth is, this constant velocity (CV) carburetor is a masterpiece of emissions-era engineering when it works correctly. But when it fails? It becomes a ticking time bomb of hesitation, flat spots, and sticky slides.

This article provides . We have cross-referenced part numbers, torque specs, and tuning parameters to give you the definitive guide to rebuilding, tuning, and troubleshooting the BS26. Part 1: What is the Mikuni BS26? (Understanding the CV Design) Before you turn a single screw, you need to understand what you are working with. The "BS" stands for Bore Size Symmetrical , and "26" refers to the 26mm venturi diameter. mikuni bs26 carburetor manual verified

By using the outlined in this article—float height of 13.0mm, pilot screw at 2.5 turns, legitimate OEM diaphragms, and a stock air box—your BS26 will start on the first choke pull in freezing weather and idle like a sewing machine.

Unlike a flat-slide racing carburetor, the BS26 is a unit. This means the throttle plate (butterfly valve) is directly connected to your throttle cable, but the slide (piston valve) is controlled by engine vacuum and a diaphragm. | Symptom | Common Forum Advice | |

The problem is not the carburetor itself; it is the floating around forums. A quick search for "Mikuni BS26 carburetor manual verified" often leads to conflicting jet sizes, incorrect float heights, and dangerous tuning advice.

Because the BS26 is a CV carb, it requires a still air box to create the correct pressure signal over the diaphragm bleed hole. If you remove the air box and install foam pods, you create turbulence that confuses the slide. | | Backfire on decel | "You have a header leak

Need a specific torque value or jet size for your exact year and model? Leave a comment below with your bike’s VIN prefix, and we will pull the verified page from the factory manual.