Buell S1 Lightning User Manual

4-11
Accelerator Pump System
See Figure 4-8. The accelerator pump system uses sudden
throttle openings (rapid acceleration) to quickly inject fuel into
the carburetor venturi; the extra fuel provides for smooth
acceleration. This fuel also assists engine operation during
cold engine warm-up when the enrichener is turned off pre-
maturely.
Rapid throttle action, during the first third of throttle travel,
causes the accelerator pump rod to depress the accelerator
pump diaphragm. This forces fuel in the pump to flow through
a fuel passage (which has a “one-way” check valve), through
the pump nozzle, and then into the venturi. When the throttle
closes, the pump rod lifts up and away from the pump
diaphragm; a spring below the diaphragm pushes the
diaphragm upward, thereby causing the lower pump cavity to
refill with fuel from the float bowl. The check valve prevents
backflow of fuel from the pump nozzle/fuel passage during
this refilling phase.
Figure 4-8. Accelerator Pump System
FUEL
Throttle
shaft
Throttle
rod
Spring
Pump
rod
Spring
Diaphragm
Check
valve
Pump
nozzle
Venturi
Pump lever

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