Buell S1 Lightning User Manual

4-8
Idle- and Low-Speed Circuit
See Figure 4-5. At idle (with the throttle plate closed and the
main air stream obstructed), engine idle speed is maintained
by fuel metered through the slow jet. Air from the slow air jet
mixes with the fuel and is delivered to the idle port at the low
pressure side of the throttle plate.
At low-speed (with the throttle plate slightly open), the transfer
ports are exposed to the low pressure side of the throttle plate,
and additional fuel is directed to the barrel of the carburetor.
During the transition period from idle speed to mid-range, the
idle and transfer ports also supply some fuel to the carburetor
barrel; this allows for a smoother transition.
The venturi opening is reduced by the low position of the vac-
uum piston. This enables initial air stream velocities to be
higher than normally attainable with fixed-venturi carburetors.
The higher air stream velocities provide improved atomization
of fuel necessary for good acceleration and driveability.
Figure 4-5. Idle- and Low-Speed Circuit
AIR/FUEL
FUEL
AIR
Spring
Diaphragm
Vacuum piston
Vacuum piston
Vacuum port
Slow air jet
Slow jet
Idle mixture
screw
Idle port
Transfer ports
Throttle plate

Buell S1 Lightning Specifications

General

Transmission	5-speed
Rear Brakes	Single 230mm disc, single-piston caliper
Compression Ratio	10.0:1
Ignition	Electronic
Engine Type	Air-cooled, four-stroke, 45° V-twin
Rear Suspension	Showa monoshock, adjustable preload, compression and rebound damping
Front Brakes	Single 340mm disc, 6-piston caliper
Seat Height	775 mm
Bore x Stroke	88.8 mm x 96.8 mm
Fuel System	Carburetor
Frame	Tubular steel
Tires	Front: 120/70 ZR17, Rear: 170/60 ZR17