Mikuni Bs26 Carburetor Manual Verified May 2026

Note: Values are for sea level (0–1,000m), 20°C ambient. Adjust for altitude/weather.

| Component | Suzuki GSX250 | Kawasaki ZZR250 | Bajaj Pulsar 220 | |-----------|---------------|-----------------|------------------| | Main Jet | #97.5 | #102 | #115 | | Pilot Jet | #35 | #38 | #40 | | Jet Needle | 5D28 (clip 3rd) | 5C30 (clip 2nd) | 6F24 (clip 3rd) | | Needle Jet | P-2 (O-2) | P-4 (O-4) | P-6 | | Pilot Screw (turns out) | 1.5 – 2.0 | 2.0 – 2.5 | 2.0 | | Float height (mm) | 13.0 ± 1 | 14.5 ± 1 | 12.8 ± 1 |

Verified check: Mikuni genuine jets are stamped with a square symbol. Aftermarket "Mikuni-style" jets often vary by 5-10% – always use genuine Keihin or Mikuni.

The BS26 uses soft aluminum body castings. Over-tightening is the #1 cause of stripped threads. mikuni bs26 carburetor manual verified

| Fastener | Verified Torque (in-lbs) | Warning | | :--- | :--- | :--- | | Float Bowl screws | 7-9 in-lbs | Use a JIS screwdriver, not Phillips. | | Top cap screws (diaphragm cover) | 4-6 in-lbs | Overtightening distorts the diaphragm sealing surface. | | Drain plug (bottom of bowl) | 13 in-lbs | Replace the copper crush washer every time. | | Choke plunger nut | Hand tight + 1/8 turn | Plastic threads—do not use tools. |

The BS26 is not very tunable – the CV design limits adjustment. Verified guidelines:

| Modification | Required change | Jet size change | |--------------|----------------|------------------| | Pod filter (no airbox) | Impossible to tune well – BS26 needs airbox restriction | +2 on main jet, raise needle 1 clip, pilot +2 sizes – but still runs poorly | | High-flow exhaust | Usually none | Only if popping on decel → +1 on pilot jet | | High altitude (>2,000m) | Drop main jet by 1 size per 1,000m | Example: #100 → #95 | Note: Values are for sea level (0–1,000m), 20°C ambient

Verified fact: The BS26’s CV system relies on airbox negative pressure. Removing the airbox almost always results in a flat spot from 3,000–5,000 RPM that no jetting can fully cure.

You do not need a new carburetor. You need a diagnostic flowchart.

| Symptom | Common Forum Advice | Verified Manual Fix | | :--- | :--- | :--- | | 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. | Verified check : Mikuni genuine jets are stamped

Here is the harsh truth verified by decades of dyno runs: The Mikuni BS26 absolutely hates pod filters.

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.

If you insist on pods (non-verified hack, but field proven):

The verified warning: You will never get a perfect idle with pods on a BS26. Suzuki's engineering notes explicitly state the air box volume (5.8 liters) is required for pressure wave stability.