This frustrating "flat spot" has a few verified causes:
Never use wires, drill bits, or welding tip cleaners to clear brass jets. These tools will gouge the soft metal, permanently altering the hole diameter and ruining your fuel calibration. 4. Line Routing and Hose Connections
Turn the pilot screw in/out in 1/2 turn increments every 10 seconds until the engine reaches its highest, steadiest idle.
This guide provides a of the Mikuni BS26 operation, essential manual tuning, and rebuilding techniques, designed to help enthusiasts restore or optimize performance. 1. Understanding the Mikuni BS26 CV Design mikuni bs26 carburetor manual verified
If the engine cuts out or loses power at wide-open throttle, change the main jet size. A white plug tip indicates a lean condition requiring a larger main jet number. A dark soot-covered plug tip indicates a rich condition requiring a smaller main jet number. Comprehensive Troubleshooting Matrix Primary Root Cause Verified Corrective Action Engine will not start; dry spark plug Clogged pilot jet or blocked fuel inlet needle valve.
Never allow carburetor cleaner to contact the rubber diaphragm, the float bowl gasket, or the fuel inlet O-rings. It will swell and ruin the rubber.
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Never clear brass jet orifices with welding tip cleaners or steel wire. Steel scratches the soft brass, enlarging the precise hole sizes permanently.
Use a caliper to measure the distance from the machined gasket mating surface (with the gasket removed) to the highest point of the float profile.
Submerge all brass pieces in commercial carburetor cleaner or an ultrasonic cleaner solution for 20 minutes. Line Routing and Hose Connections Turn the pilot
| 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. |
#95 to #110 (Varies by vehicle manufacturer) Pilot Jet (Stock standard): #15 to #22.5