Buell S1 Lightning Workshop Manual page 208

Starting Circuit
See Figure 4-4. The starting circuit consists of a cable-actu-
ated enrichener valve and converging fuel and air passages
in the carburetor body.
The enrichener air/fuel passage opens to the carburetor ven-
turi, where low pressure exists when the engine is running.
Fuel in the carburetor float bowl and air in the enrichener air
inlet are vented to atmosphere and are at atmospheric pres-
sure (greater pressure than in the carburetor venturi).
Enrichener
air inlet
Enrichener
valve cable
AIR
FUEL
AIR/FUEL
When the enrichener knob is pulled outward, the enrichener
valve opens the air/fuel passage to the low pressure carbure-
tor venturi. Fuel in the float bowl, at atmospheric pressure,
flows upward through a metering enrichener jet and then
through a passage to the lower pressure enrichener valve
chamber. Air in the enrichener air inlet, at atmospheric pres-
sure, also flows into the lower pressure enrichener valve
chamber and mixes with the incoming fuel. The resulting air/
fuel mixture flows through the air/fuel passage into the carbu-
retor venturi, effectively increasing the amount of fuel deliv-
ered to the combustion chambers.
Figure 4-4. Starting Circuit
Enrichener
valve
Air/fuel
passage
Enrichener
jet
4-7