Carburetor Jet Drilling: How to Drill Walbro Jets

Drilling carburetor jets requires precision and the right tools to avoid damaging the jet or altering fuel flow incorrectly. This process is often done to fine-tune air-fuel mixture for performance modifications.

Tools and Materials Needed

  • Carburetor jet drill bits (typically 0.3mm to 0.8mm sizes)
  • Pin vise or micro drill chuck
  • Magnifying glass or loupe
  • Carburetor cleaner
  • Compressed air
  • Measuring tools (micrometer or caliper)

    • Step-by-Step Process

    1. Remove the jet from the carburetor body
    2. Clean the jet thoroughly with carburetor cleaner
    3. Secure the jet in a pin vise
    4. Align the drill bit with the existing hole
    5. Drill slowly with minimal pressure
    6. Measure the hole diameter
    7. Clean and reinstall the jet

    Common Jet Sizes and Effects

    Jet Size Effect on Mixture Typical Use
    0.3mm Leaner Stock, mild mods
    0.5mm Balanced Moderate performance
    0.7mm Richer High performance

    Safety and Precision Tips

    • Work in a clean, well-lit area
    • Use magnification to see the jet clearly
    • Drill in small increments, checking size often
    • Never force the drill bit
    • Consider buying pre-drilled jets if unsure

    Testing After Modification

    After drilling, test the carburetor under load conditions. Check for proper throttle response, exhaust color, and engine temperature. Make adjustments as needed for optimal performance.