WCFB Troubleshooting Page 2

Why Doesn’t Adjusting Idle Mixture Screws Make any Difference?

The idle mixture screws adjust the amount of air/fuel mixture that goes up to the venturi at idle. When adjusting the screws doesn’t change the RPM then it means there is a problem with either the air, or the amount of fuel.

  • The mixture screw may be bent, or damaged. Look for any scoring on the tip of the screw. This is most often caused by turning the screw in too hard.
  • The air and/or fuel passage is plugged. Squirt carburetor cleaner into the screws hole, blocking the transition hole in the bore. Watch the venturi to see if the carb cleaner makes it through.
  • There could be a vacuum leak. Check the mounting gasket and any other vacuum sources.
  • Make sure the float bowl gasket is correct and not allowing air through the gasket.
  • Check for a bent metering rod.
  • A warped carburetor could be allowing air to sneak in through the float bowl gasket.
  • Make sure the metering rods are adjusted.

Surges at cruising, or high speeds

  • Clogged main jets.
  • Low fuel pump pressure, or volume. Test for 4 lbs.
  • Dirty air bleeds.
  • Dirty filter, or filter screens.
  • Float out of adjustment.

With Expansion Pump

Carter WCFB Carburetor Kit

With Solid Pump


Updated on 04/13/2022

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