PRINCIPLES GASOLINE/DIESEL FUEL SYSTEMS - OD1620 - LESSON 1/TASK 2
c. HighSpeed and HighSpeed Enrichment Circuits.
(1) Purpose. The highspeed circuit supplies the fuelair mixture to
the engine during medium to full throttle valve opening. The highspeed
circuit gradually will take over from the lowspeed circuit as the throttle
is depressed. The carburetor is designed to provide approximately a 16:1 to
17:1 airfuel ratio under normal, steady speed conditions. The highspeed
enrichment circuit will enrich the mixture to approximately 11:1 to 12:1 if
a heavy demand is placed on the engine.
(2) Operation (figure 16). The highspeed circuit takes its gasoline
from the float bowl through the main jet. The gasoline is fed through a
passageway to the discharge nozzle, where it sixes with the air in the
venturi. Opening the throttle valve and accelerating the engine speed
increases the airflow in the venturi, which causes a proportional increase
in the amount of gasoline from the discharge nozzle. The highspeed
enrichment system increases the fuel flow to the discharge nozzle by either
increasing the main jet
FIGURE 16. HIGHSPEED SYSTEMS.