Holley 1940 Idle Circuit

This is the idle circuit of the Holley 1940 1 barrel carburetor.

The idle circuit begins at the main jet, through which fuel enters the idle well. The fuel level is controlled by the float system and anytime the throttle plate is in closed or almost closed, fuel is drawn through the idle tube from the idle well. Fuel travels through the idle tube, then mixed with air from the idle bleed and down to the idle discharge. As the throttle starts to open extra fuel is introduced through the idle transfer slot to supply more needed fuel.

• Make sure all passages are open. You may have to run thin wire down them to be sure.
• Is the idle air bleed hole open in the throat?
• Is the hole that leads from the idle mixture screw to the bore open?
• Check the idle mixture screw for any signs of damage. Buff the screw with a wire wheel. Any grooves on the tip? Replace it.
• Make sure the Idle aspirator passage is open.
• The idle air bleed does not come out and has a very small passage. Using compressed air make sure it goes through.