Ford LRG-423 Service Manual page 134

03-25 Auxiliary Systems
03-25
ZENITH MODEL #33 CARBURETOR OPERATION AND SERVICE (Continued)
SECONDARY IDLE
DISCHARGE HOLE
IDLE AIR BLEED
IDLE JET AND
PICK-UP TUBE
IDLE ADJUSTING
IDLE SYSTEM
PPD0012
The discharge of the idle fuel into the air stream at
curb idle is controlled by the idle adjusting needle in
the primary idle discharge hole. Turning the needle in
(clockwise) restricts the primary discharge hole to
provide a leaner mixture. Turning the needle out
(counterclockwise) allows a richer mixture.
As the throttle plate opens, extra fuel is discharged
from the secondary idle discharge holes as the throttle
plate passes them. This hole is precisely located from
the closed throttle plate with the size and location
depending on fuel requirements. As the throttle plate is
opened wider, the idle system gradually ceases to
function. The delivery of fuel through the high speed
system increases as the throttle plate is advanced.
Although the delivery of fuel through the idle system
diminishes as the throttle plate approaches the wide
open position, it continues to deliver a small volume of
fuel contributing to the fuel delivered by the high speed