How to Remove a Seized Mixture Screw (Without Ruining Your Carburettor)

A stuck or snapped mixture screw is one of the most common issues found in older Mikuni, Keihin or CV carburettors. Bandits, CB series, SRADs and anything previously tinkered with are especially prone to it. The screws seize due to corrosion and heat cycles, and when they’re forced with a screwdriver the slot rounds off or the thin neck snaps.

Here’s the correct way to extract a seized mixture screw without damaging the carb body.

Tools You’ll Need

  • Mini handheld drill or Dremel
  • Burr or engraving bit
  • 3mm drill bit
  • Small hammer
  • Left-handed extractor or precision pick set
  • Compressed air and carb cleaner


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Step-by-Step Removal Procedure

1. Flatten the top of the broken screw

If it has snapped, gently shave the surface flat to create a clean centre point.

2. Use a burr bit to make a pilot mark

This stops the drill bit wandering and protects the carb casting.

3. Drill carefully with a 3mm bit

Drill straight down the middle until you reach the bottom of the threaded section. Do not go deeper or you’ll damage the tapered seat.

4. Tap in an extractor or pick

Lightly tap in a screw extractor or sharpened pick and turn anti-clockwise until the shell backs out.

5. Clean the threads and passage

Flush the area with carb cleaner and compressed air, then chase the threads if needed.



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What Not to Do

  • Don’t heat the carb body as the alloy expands more than brass and tightens the screw

  • Don’t force it with a bigger screwdriver

  • Don’t drill with a large bit


If the screw is already butchered, send the carb in. We extract these daily and can even repair the thread when needed.